A total solar eclipse is unlike anything you've seen in your life. As totality approaches, you will see the astonishing sight of day turning to night and the Sun's corona blazing in the sky. This is truly a great American eclipse because totality will sweep the nation from the Pacific to the Atlantic. Nearly everyone in the US can reach this total solar eclipse within one day's drive. An eclipse is a cosmic billiard shot — the Sun, Moon, and Earth line up to reveal the Sun's atmosphere, it's corona. Eclipses on Earth occur only because of an amazing celestial coincidence. ||||| Editor's note: The Great American Solar Eclipse was on Aug. 21, 2017. It swept across the continental United States from Oregon to Georgia. See our full coverage. Another total solar eclipse will be seen across the United States in 2024. 
  
 A solar eclipse occurs when the moon gets between Earth and the sun, and the moon casts a shadow over Earth. A solar eclipse can only take place at the phase of new moon, when the moon passes directly between the sun and Earth and its shadows fall upon Earth’s surface. But whether the alignment produces a total solar eclipse, a partial solar eclipse or an annular solar eclipse depends on several factors, all explained below. 
  
 The fact that an eclipse can occur at all is a fluke of celestial mechanics and time. Since the moon formed about 4.5 billion years ago, it has been gradually moving away from Earth (by about 1.6 inches, or 4 centimeters per year). Right now the moon is at the perfect distance to appear in our sky exactly the same size as the sun, and therefore block it out. But this is not always true. 
  
 The next solar eclipse is a partial eclipse that will take place on Jan. 5-6, 2019. It will be visible from northeast Asia, the Pacific Ocean and parts of Alaska. A total solar eclipse will occur on July 2, 2019 in South America. To find out about upcoming solar eclipses and how to see them, check our guide. 
  
 How Solar Eclipses Work: When the moon covers up the sun, skywatchers delight in the opportunity to see a rare spectacle. See how solar eclipses occur in this Space.com infographic Credit: Karl Tate, SPACE.com Contributor 
  
 There are four types of solar eclipses: total, annular, partial and hybrid. Here’s what causes each type: 
  
 Total solar eclipses 
  
 These are a happy accident of nature. The sun's 864,000-mile diameter is fully 400 times greater than that of our puny moon, which measures just about 2,160 miles. But the moon also happens to be about 400 times closer to Earth than the sun (the ratio varies as both orbits are elliptical), and as a result, when the orbital planes intersect and the distances align favorably, the new moon can appear to completely blot out the disk of the sun. On the average a total eclipse occurs somewhere on Earth about every 18 months. 
  
 There are actually two types of shadows: the umbra is that part of the shadow where all sunlight is blocked out. The umbra takes the shape of a dark, slender cone. It is surrounded by the penumbra, a lighter, funnel-shaped shadow from which sunlight is partially obscured. 
  
 During a total solar eclipse, the moon casts its umbra upon Earth's surface; that shadow can sweep a third of the way around the planet in just a few hours. Those who are fortunate enough to be positioned in the direct path of the umbra will see the sun's disk diminish into a crescent as the moon's dark shadow rushes toward them across the landscape. 
  
 During the brief period of totality, when the sun is completely covered, the beautiful corona — the tenuous outer atmosphere of the sun — is revealed. Totality may last as long as 7 minutes 31 seconds, though most total eclipses are usually much shorter. 
  
 On Jan. 4, 2011, the moon passed in front of the sun in a partial solar eclipse - as seen from parts of Earth. Here, the joint Japanese-American Hinode satellite captured the same breathtaking event from space. The unique view created what's called an annular solar eclipse. Credit: Hinode/XRT 
  
 Partial solar eclipses 
  
 A partial solar eclipse occurs when only the penumbra (the partial shadow) passes over you. In these cases, a part of the sun always remains in view during the eclipse. How much of the sun remains in view depends on the specific circumstances. 
  
 Usually the penumbra gives just a glancing blow to our planet over the polar regions; in such cases, places far away from the poles but still within the zone of the penumbra might not see much more than a small scallop of the sun hidden by the moon. In a different scenario, those who are positioned within a couple of thousand miles of the path of a total eclipse will see a partial eclipse. 
  
 The closer you are to the path of totality, the greater the solar obscuration. If, for instance, you are positioned just outside of the path of the total eclipse, you will see the sun wane to a narrow crescent, then thicken up again as the shadow passes by. 
  
 Annular solar eclipses 
  
 An annular eclipse, though a rare and amazing sight, is far different from a total one. The sky will darken ... somewhat; a sort of weird “counterfeit twilight” since so much of the sun still shows. The annular eclipse is a subspecies of a partial eclipse, not total. The maximum duration for an annular eclipse is 12 minutes 30 seconds. 
  
 However, an annular solar eclipse is similar to a total eclipse in that the moon appears to pass centrally across the sun. The difference is, the moon is too small to cover the disk of the sun completely. Because the moon circles Earth in an elliptical orbit, its distance from Earth can vary from 221,457 miles to 252,712 miles. But the dark shadow cone of the moon’s umbra can extend out for no longer than 235,700 miles; that’s less than the moon’s average distance from Earth. 
  
 So if the moon is at some greater distance, the tip of the umbra does not reach Earth. During such an eclipse, the antumbra, a theoretical continuation of the umbra, reaches the ground, and anyone situated within it can look up past either side of the umbra and see an annulus, or “ring of fire” around the moon. A good analogy is putting a penny atop a nickel, the penny being the moon, the nickel being the sun. 
  
 Hybrid solar eclipses 
  
 These are also called annular-total (“A-T”) eclipses. This special type of eclipse occurs when the moon’s distance is near its limit for the umbra to reach Earth. In most cases, an A-T eclipse starts as an annular eclipse because the tip of the umbra falls just short of making contact with Earth; then it becomes total, because the roundness of the planet reaches up and intercepts the shadow tip near the middle of the path, then finally it returns to annular toward the end of the path. 
  
 Because the moon appears to pass directly in front of the sun, total, annular and hybrid eclipses are also called “central” eclipses to distinguish them from eclipses that are merely partial. 
  
 Of all solar eclipses, about 28 percent are total; 35 percent are partial; 32 percent annular; and just 5 percent are hybrids. 
  
 Eclipses do not happen at every new moon, of course. This is because the moon’s orbit is tilted just over 5 degrees relative to Earth’s orbit around the sun. For this reason, the moon’s shadow usually passes either above or below Earth, so a solar eclipse doesn’t occur. 
  
 But as a rule, at least twice each year (and sometimes as many as five times in a year), a new moon will align itself in just such a way to eclipse the sun. That alignment point is called a node. Depending on how closely the new moon approaches a node will determine whether a particular eclipse is central or partial. And of course, the moon’s distance from the Earth — and to a lesser degree, Earth’s distance from the sun — will ultimately determine whether a central eclipse is total, annular or a hybrid. 
  
 And these alignments don’t happen haphazardly, for after a specific interval of time, an eclipse will repeat itself or return. This interval is known as the Saros cycle and was known as far back as the days of the early Chaldean astronomers some 28 centuries ago. The word Saros means “repetition” and is equal to 18 years, 11⅓ days (or a day less or more depending on the number of leap years that have intervened). After this interval, the relative positions of the sun and moon relative to a node are nearly the same as before. That third of a day in the interval causes the path of each eclipse of a series to be displaced in longitude a third of the way around Earth to the west with respect to its predecessor. 
  
 For example, on March 29, 2006, a total eclipse swept across parts of western and northern Africa and then across southern Asia. One Saros later, on April 8, 2024, this eclipse will recur, except instead of Africa and Asia, it will track across northern Mexico, the central and eastern United States and the Maritime provinces of Canada. 
  
 You should never look directly at the sun, but there are ways to safely observe an eclipse. See how to safely observe a solar eclipse with this Space.com infographic Credit: Karl Tate, SPACE.com Contributor 
  
 As a solar eclipse approaches, the mainstream media often will provide a variety of warnings and advisories against looking at the sun with bare eyes, as blindness could ensue. This has given most people the idea that eclipses are dangerous. 
  
 Not so! 
  
 It’s the sun that is dangerous — all the time! The sun constantly emits invisible infrared rays that can damage your eyes. Ordinarily, we have no reason to gaze at the sun. An eclipse gives us a reason, but we shouldn’t. 
  
 There are safe ways, however . . . 
  
 By far, the safest way to view a solar eclipse is to construct a “pinhole camera.” A pinhole or small opening is used to form an image of the sun on a screen placed about 3 feet (or about 1 meter) behind the opening. Binoculars or a small telescope mounted on a tripod can also be used to project a magnified image of the sun onto a white card. The farther away the card, the larger you can focus the image. Look for sunspots. Notice that the sun appears somewhat darker around its limb or edge. This method of solar viewing is safe so long as you remember not to look through the binoculars or telescope when they are pointed toward the sun; put another way, never look directly at the sun when any part of its blindingly bright surface is visible. 
  
 A variation on the pinhole theme is the “pinhole mirror.” Cover a pocket-mirror with a piece of paper that has a ¼-inch hole punched in it. Open a sun-facing window and place the covered mirror on the sunlit sill so it reflects a disk of light onto the far wall inside. The disk of light is an image of the sun’s face. The farther away from the wall is the better; the image will be only 1 inch across for every 9 feet (or 3 centimeters for every 3 meters) from the mirror. Modeling clay works well to hold the mirror in place. Experiment with different-sized holes in the paper. Again, a large hole makes the image bright, but fuzzy, and a small one makes it dim but sharp. Darken the room as much as possible. Be sure to try this out beforehand to make sure the mirror’s optical quality is good enough to project a clean, round image. Of course, don’t let anyone look at the sun in the mirror. 
  
 If you’re around leafy trees, look at the shadow cast by them during the partial phases. What do you see? Is it worth a photograph? You will see scores of partially eclipsed suns projected through pinhole gaps between the leaves. This is caused by diffraction, a property of light. According to Vince Huegele, an optical physicist at the NASA Marshall Space Flight Center, the light rays do not shoot straight by the rim of the gaps, or a pinhole, but bend around the edge. This wave effect creates a pattern of rings that resembles a bull's eye. 
  
 Acceptable filters for unaided visual solar observations include aluminized Mylar. Some astronomy dealers carry Mylar filter material specially designed for solar observing. Also acceptable is shade 14 arc-welder’s glass, available for just a few dollars at welding supply shops. Of course, it is always a good idea to test your filters and/or observing techniques before eclipse day. 
  
 Unacceptable filters include sunglasses, old color film negatives, black-and-white film that contains no silver, photographic neutral-density filters and polarizing filters. Although these materials have very low visible-light transmittance levels, they transmit an unacceptably high level of near-infrared radiation that can cause a thermal retinal burn. The fact that the sun appears dim, or that you feel no discomfort when looking at the sun through these types of filters, is no guarantee that your eyes are safe. 
  
 There is one time when you can safely look directly at the sun: during a total eclipse, when the sun's disk is entirely covered. During those few precious seconds or minutes, the magnificent corona shines forth in all its glory surrounding the darkened sun; a marvelous fringe of pearly white light. It differs in size, in tints and patterns from eclipse to eclipse. It is always faint and delicate, with a sheen like a pale aurora. It has a variable appearance. Sometimes it has a soft continuous look; at other times, long rays of it shoot out in three or four directions. It may stand out from the disk in filmy petals and streamers. But when the sun begins to again emerge into view, the corona quickly disappears and you’ll need to protect your eyes once again. 
  
 This photo of the partial solar eclipse of Sept. 13, 2015, was snapped by astrophotographer K.J. Mulder from his home in South Africa. Credit: K.J. Mulder/Worlds in Ink 
  
 As best as we can determine, the earliest record of a solar eclipse occurred over four millennia ago. In China, it was believed that the gradual blotting out of the sun was caused by a dragon who was attempting to devour the sun, and it was the duty of the court astronomers to shoot arrows, beat drums and raise whatever cacophony they could to frighten the dragon away. 
  
 In the ancient Chinese classic Shujing (or Book of Documents) is the account of Hsi and Ho, two court astronomers who were caught completely unaware by a solar eclipse, having gotten drunk just before the event began. In the aftermath, Zhong Kang, the fourth emperor of the Xia dynasty ordered that Hsi and Ho be punished by having their heads chopped off. The eclipse in question was that of Oct. 22 in the year 2134 B.C. 
  
 In the Bible, in the book of Amos 8:9, are the words, “I will cause the sun to go down at noon, and I will darken the Earth in the clear day.” Biblical scholars believe this is a reference to a celebrated eclipse observed at Nineveh in ancient Assyria on June 15, 763 B.C. An Assyrian tablet also attests to the event. 
  
 A solar eclipse even stopped a war. 
  
 According to the historian Herodotus, there was a five-year war that raged between the Lydians and the Medes. As the war was about to move into its sixth year, a Greek sage, Thales of Miletus foretold to the Ionians that the time was soon approaching when day would turn to night. On May 17, 603 B.C. the sun faded away just as Thales had alluded that it would. So believing that it was a sign from above, the combatants called a truce, which was cemented by a double marriage, for, as Herodotus wrote: “Without some strong bond, there is little of security to be found in men’s covenants.” 
  
 And giving new meaning to the term, “Scared to death,” is the timid emperor Louis of Bavaria, the son of Charlemagne, who witnessed an unusually long total eclipse of the sun on May 5, A.D. 840, which lasted for over five minutes. But no sooner had the sun begun to emerge back into view, Louis was so overwhelmed by what he had just seen that he died of fright! 
  
 Astronomers have learned much by studying eclipses and by the 18th century, observations of solar eclipses were recognized as providing veritable treasure troves of astronomical information, though sometimes getting that information wasn’t easy. 
  
 Samuel Williams, a professor at Harvard, led an expedition to Penobscot Bay, Maine, to observe the total solar eclipse of Oct. 27, 1780. As it turned out, this eclipse took place during the Revolutionary War, and Penobscot Bay lay behind enemy lines. Fortunately, the British granted the expedition safe passage, citing the interest of science above political differences. 
  
 And yet in the end, it was all for naught. 
  
 Williams apparently made a crucial error in his computations and inadvertently positioned his men at Islesboro — just outside the path of totality — likely finding this out with a heavy heart when the narrowing crescent of sunlight slid completely around the dark edge of the moon and then started to thicken! 
  
 During a total solar eclipse, a few ruby-red spots may seem to hover around the jet-black disk of the moon. Those are solar prominences, tongues of incandescent hydrogen gas rising above the surface of the sun. During the total eclipse of Aug. 18, 1868, the French astronomer Pierre Janssen trained his spectroscope on the prominences and discovered a new chemical element. Two English astronomers, J. Norman Lockyer and Edward Frankland, later named it “helium,” from the Greek helios (the sun). The gas was not identified on Earth until 1895. 
  
 And because sunlight is blocked during a total eclipse, some of the brighter stars and planets can be observed in the darkened sky. Under such conditions astronomers were able to test part of Einstein’s now-celebrated general theory of relativity. That theory predicted that light from stars beyond the sun would bend from a straight path in a certain way as it passed the sun. The positions of stars photographed near the sun’s edge during a total eclipse on May 29, 1919, were compared with photographs of the same region of the sky taken at night; the results strongly supported Einstein’s theory. 
  
 Our modern technology now allows astronomers to make most of the observations that once had to await an eclipse. But a total eclipse of the sun will always remain among the most impressive of natural spectacles and is a sight that will always be remembered. Be sure to put it on your bucket list; you will not be disappointed. ||||| Two years from today, on Aug. 21, 2017, North Americans will get an opportunity to observe nature's greatest sky show. 
  
 Picture this: The day starts off bright and sunny. Then, a bit later, you begin to notice that, although it is still sunny, the day doesn't seem quite so bright. And still a little while later, it almost seems like some big storm is brewing. Then, suddenly, and without any warning, the midsummer day turns strangely dark. 
  
 A few stars come out. Birds and animals become confused and quickly head home to sleep. Night insects begin to chirp. All around the horizon, there is a strange yellow-orange glow resembling a weird sunset. And meanwhile, up in the sky where the sun should be, there appears instead a jet-black disk surrounded by a softly glowing halo. [Amazing 2015 Solar Eclipse Photos] 
  
 Then, just as suddenly, the sky brightens up. The stars disappear, birds and animals awaken, and the sun returns. 
  
 What you have just witnessed is a total eclipse of the sun. 
  
 This total solar eclipse of 2017 will be the first time in nearly four decades that such an event will be visible so close to home. "Close," of course, is a relative term. But for most Americans, this spectacular phenomenon will occur literally in their own backyards. 
  
 Contrary to popular belief, totalsolar eclipses are not particularly rare. Astronomers predict 68 to take place during the present century — one about every 17.6 months. On such occasions, the moon casts its dark, slender cone of shadow (called the umbra) upon the Earth's surface. [How Solar Eclipses Work (Infographic)] 
  
 The track traced by the moon's umbra can run for many thousands of miles, but it's also very narrow — at most, about 167 miles (268 kilometers) wide. For this reason, it has been calculated that, on average, a total eclipse of the sun is visible from the same spot on Earth only once in about every 375 years. 
  
 In recent years, for instance, assiduous eclipse chasers had to travel to remote locations such as Ellesmere Island in Nunavut, Canada (2008), Easter Island (2010) or the Norwegian archipelago of Svalbard (2015). 
  
 Map showing the path of totality across the United States for the total solar eclipse of Aug. 21, 2017. Credit: Fred Espenak/NASA GSFC 
  
 But Aug. 21, 2017, will mark the first time this century, and the first time since 1979, that a total solar eclipse will cross the contiguous (lower 48) United States (Alaska had its turn in 1990; Hawaii in 1991). And for the very first time, the shadow track — better known as the "path of totality" — will sweep only over the United States and no other country, leading some people to refer to this upcoming event as "The Great American Eclipse." 
  
 Many Americans taking full advantage of this event's close proximity to their homes will have a golden opportunity to witness firsthand one of the most beautiful and most exciting of nature's sky events. The total eclipse will be seen by an estimated 12 million people who fortuitously live within the totality path. However, the number of people who are within just one day's drive of the totality zone is probably around 200 million. [How to Safely Photograph the Sun (Photo Guide)] 
  
 Not since 1970 has there been an opportunity to see a total solar eclipse in such easily accessible and widespread areas of the United States. There have been a couple of limited opportunities, such as in 1972 (Quebec and the adjacent Canadian Maritime Provinces) and 1979 (the Pacific Northwest and Northern Plains), but the areas of visibility were either limited or somewhat difficult to reach. And not until April 2024 will there be another opportunity comparable to that offered on Aug. 21, 2017. 
  
 Also, for the first time since 1918, the moon's dark shadow will sweep across the U.S. from coast to coast. At local sunrise on this third Monday in August, the shadow of the moon will first touch the Earth at a point in the North Pacific Ocean, about 1,500 miles (2,414 km) northwest of the Hawaiian Islands. Then, for 3 hours and 13 minutes, the shadow will race first east-northeast, then east and finally southeast, along the way darkening a narrow strip of the North American continent. 
  
 Initially, the shadow will traverse nothing but wide-open ocean for 28 minutes. Finally, it will make landfall along the coast of Oregon at the community of Lincoln Beach. Traversing the United States, the total eclipse will be visible within a path of darkness stretching from Oregon and then on through Idaho, Wyoming, Nebraska, Kansas, Missouri, Illinois, Kentucky, Tennessee, Georgia, North Carolina and, finally, South Carolina. 
  
 The path will average 67 miles (108 km) in width, but while moving through western Kentucky, about 12 miles (19 km) northwest of the town of Hopkinsville, the shadow's size will widen to a maximum of 71 miles (114 km). 
  
 Because the moon's shadow is moving at such a tremendous speed, totality cannot last very long in any one place. The duration of the total phase is always longest along the center of the shadow's path. As an observer moves away from the center, the duration of totality time decreases, becoming zero along the path's edges. [Video: How Total Solar Eclipse Photos Help Astronomers] 
  
 Right at the Oregon coastline, totality lasts 1 minute and 59 seconds, as the shadow will be traveling at more than three times the speed of sound (2,400 mph, or 3,900 km/h). Heading southeast along the center line, the totality time slowly lengthens, reaching a maximum of 2 minutes and 40.3 seconds at a spot in southern Illinois about a dozen miles (about 20 km) southeast of the city of Carbondale. 
  
 The shadow — which, at this point, has slowed to 1,450 mph (2,330 km/h) — then begins to increase in speed, and the duration of totality subsequently begins to diminish. Indeed, when it arrives at the South Carolina coastline, the duration of totality will have dropped to 2 minutes and 34 seconds. The shadow then exits out to sea, finally leaving the Earth 75 minutes later at local sunset in the North Atlantic Ocean, 390 miles (627 km) to the southwest of the island nation of Cape Verde. 
  
 Notable cities inside the totality path include Idaho Falls, Idaho; Casper, Wyoming; Grand Island, Nebraska; Lincoln, Nebraska; Columbia, Missouri; Nashville, Tennessee; Columbia, South Carolina; and Charleston, South Carolina. The metropolitan areas of Kansas City, Missouri, and St. Louis are right on the edge of the totality path. 
  
 Warning: Never stare directly at the sun, either with your unaided eye or through telescopes and binoculars, without proper protection. Serious eye damage can occur. Solar eclipse observers and astronomers use special filters to safely observe the sun. 
  
 Weather experts have performed studies to help observers pick the best opportunity for cloudless skies in and near the path of totality on Aug. 21, 2017. 
  
 The best chances for a clear look appear to be in the area running from western Oregon through Wyoming, where, on average, the odds are on the order of about 70 percent. Going farther east, the odds of clear skies gradually diminish; from Kentucky to the Atlantic coast, it's just about a coin toss for favorable weather: just 50-50. 
  
 Starting the week before, the National Weather Service will provide increasingly reliable forecasts, which will enable people to choose a location where the chances of a cloudy sky are low. 
  
 Surrounding the dark umbra is the penumbra, or partial shadow. It will also be conical but much larger — nearly 6,000 miles (9,700 km) in diameter. The penumbra is simply the half shadow that lies outside every deep shadow, whether it is cast by the moon or a house. Wherever the penumbra falls, a partial eclipsewill occur. 
  
 All of North America will be inside the penumbra, causing a rather large partial eclipse for much of the U.S. and portions of southwest Canada. The closer you station yourself to the path of totality, the greater the magnitude of the partial eclipse will be. When watching the partial phases, observers should take precautions while viewing the still blindingly bright sun. 
  
 A number of large cities will lie just outside the totality zone and will see the sun cut down to an exceedingly thin sliver of light. These include Portland, Oregon; Omaha, Nebraska; Chattanooga, Tennessee; and Atlanta. From these cities, a strangely weird twilight effect will fall for a couple of minutes. 
  
 But a partial solar eclipse pales in comparison to a total one, even when 99 percent of the sun's disk is obscured. The great show can only begin at the moment when the last speck of sunlight is extinguished. And only when it's in total eclipse is the sun perfectly safe to look at; only inside the totality path itself can you witness the full grandeur of the eclipse. For that reason, many people will likely journey to position themselves within the path. 
  
 Many of us take the sun for granted, giving it little thought until it scorches our skin or gets in our eyes. But our star is a fascinating and complex object, a gigantic fusion reactor that gives us life. How much do you know about the sun? Start the Quiz 0 of 10 questions complete 
  
 Solar Quiz: How Well Do You Know Our Sun? Many of us take the sun for granted, giving it little thought until it scorches our skin or gets in our eyes. But our star is a fascinating and complex object, a gigantic fusion reactor that gives us life. How much do you know about the sun? 0 of questions complete 
  
 Without a doubt, the "All American Eclipse" will be one of the big news stories of 2017. 
  
 The major news networks will certainly deploy teams of cameras and reporters along the totality path and will follow the moon's umbra during its 90-minute sweep across the contiguous United States. Media coverage — at least for this one day — could be reminiscent of the coverage accompanying the first flights of the space shuttle. 
  
 In short, the third Monday in August 2017 will be an amazing day. Mark your calendars! 
  
 2017 ECLIPSE WEBSITES: 
  
 http://eclipse.gsfc.nasa.gov/SEgoogle/SEgoogle2001/SE2017Aug21Tgoogle.html 
  
 http://www.greatamericaneclipse.com/eclipse-2017/ 
  
 http://www.eclipse2017.org/2017/path_through_the_US.htm 
  
 http://aa.usno.navy.mil/data/docs/Eclipse2017.php 
  
 http://www.shadowandsubstance.com/2017/2017e.html 
  
 Editor's note: If you have a skywatching photo that you'd like to share for a possible story or image gallery, send images and comments in to Space.com at spacephotos@space.com. 
  
 Joe Rao serves as an instructor and guest lecturer at New York's Hayden Planetarium. He writes about astronomy for Natural History magazine, the Farmer's Almanac and other publications, and he is also an on-camera meteorologist for News 12 Westchester, New York.Follow us @Spacedotcom, Facebook and Google+. Original article on Space.com. ||||| WASHINGTON, Aug. 22 (UPI) -- Mark your calendars for Aug. 21, 2017. That's when all of North America will get a once-in-a-lifetime glimpse at a total solar eclipse. 
  
 The Great American Eclipse, as its been dubbed, will be visible to millions across the United States for the first time in nearly four decades. It will mark the first time this century a total solar eclipse will cross through the contiguous United States. It's also the first time the shadow track, called the path of totality, will sweep across the U.S. and no other country. About 200 million people will be able to reach the path of the eclipse, which will sweep the nation from South Carolina to Oregon, within a one-day drive. 
  
 Officials in Hopkinsville, Ky., are calling it the largest event to hit the town of 32,000. The town will experience the longest period of totality of any city at 2 minutes and 40 seconds. City leaders are anticipating up to 50,000 visitors will bring some $23.6 million into the area. They recently unveiled the city's logo for the event and are planning for days-long festivities. 
  
 "It is a unique opportunity and it's our great excuse to roll out the red carpet and be the best version of Hopkinsville we can possibly be," said Mayor Carter Hendricks. "Science has given us the best viewing location just north of Hopkinsville. It is up to us to promote properly so people want to come and be here." |||||

Write a summary.
– Ever dreamed of seeing the sky darken and the stars twinkle in the middle of a summer's day? Then mark your calendar for Aug. 21, 2017, because if you're in the US the chances are good that you'll be among the 200 million or so people within a day's drive of the country's first total eclipse of the sun since 1979, reports Space.com. While total solar eclipses are more common than many realize, with 68 this century, this eclipse will be the first since 1918 where the moon's shadow—the so-called "path of totality"—will sweep across the US from coast to coast. It's being called the Great American Eclipse because it will be visible from no other country on the planet. Total eclipses are technically "a fluke of celestial mechanics and time," adds Space.com, because right now the moon, which is gradually moving away from Earth, happens to be the perfect distance to appear equal in size to the sun. The moon's shadow will totally block the sun for the longest duration, two minutes and 40 seconds, just outside of Hopkinsville, Ky., and is being hailed as the largest event to ever hit the town of 32,000 people, reports UPI. But the best bet for clear viewing is said to be in Oregon, where totality will only last 2 minutes but there's a 70% chance of clear skies, as opposed to just 50% from Kentucky east through South Carolina. The path of totality will average 67 miles in width, with a few notable cities in its path, including Lincoln, Neb., Columbia, Mo., and Nashville, Tenn. To those outside the path of totality but in the continental US, a partial eclipse should still be visible, though the sky will be considerably less dark. (The last total solar eclipse was in March.)
En total solförmörkelse är olik allt du har sett i ditt liv. När totaliteten närmar sig kommer ni att se den häpnadsväckande synen av dag som förvandlas till natt och solens korona flammar på himlen. Detta är verkligen en stor amerikansk solförmörkelse eftersom totaliteten kommer att svepa nationen från Stilla havet till Atlanten. Nästan alla i USA kan nå denna totala solförmörkelse inom en dags drift. En solförmörkelse är ett kosmiskt biljardskott – solen, månen och jorden radas upp för att avslöja solens atmosfär, det är korona. Eklipser på jorden inträffar bara på grund av ett fantastiskt himmelskt sammanträffande. Redaktörens anmärkning: The Great American Solar Eclipse var den 21 augusti 2017. Den svepte över kontinentala USA från Oregon till Georgia. Se vår fulla täckning. En annan total solförmörkelse kommer att ses över hela USA år 2024. En solförmörkelse inträffar när månen kommer mellan jorden och solen, och månen kastar en skugga över jorden. En solförmörkelse kan bara ske vid nymånens fas, då månen passerar direkt mellan solen och jorden och dess skuggor faller ner på jordens yta. Men huruvida justeringen ger upphov till en total solförmörkelse, beror en partiell solförmörkelse eller en annulär solförmörkelse på flera faktorer, som alla förklaras nedan. Att en förmörkelse alls kan inträffa är en lyckträff av himmelsmekanik och tid. Sedan månen bildades för omkring 4,5 miljarder år sedan har den gradvis flyttats bort från jorden (med omkring 1,6 tum, eller 4 centimeter per år). Just nu är månen på det perfekta avståndet för att visa sig på vår himmel exakt lika stor som solen, och därför blockera den. Men detta är inte alltid sant. Nästa solförmörkelse är en partiell solförmörkelse som kommer att äga rum den 5–6 januari 2019. Den kommer att synas från nordöstra Asien, Stilla havet och delar av Alaska. En total solförmörkelse kommer att inträffa den 2 juli 2019 i Sydamerika. För att ta reda på om kommande solförmörkelser och hur man ser dem, kolla vår guide. Hur solförmörkelser fungerar: När månen täcker över solen gläder sig skyskådare åt möjligheten att se ett sällsynt skådespel. Se hur solförmörkelser uppstår i denna Space.com infographic Credit: Karl Tate, SPACE.com Bidragsgivare Det finns fyra typer av solförmörkelser: totalt, annulärt, partiellt och hybridt. Här är vad som orsakar varje typ: Total solförmörkelser Dessa är en lycklig olycka av naturen. Solens diameter på 864 000 mil är helt 400 gånger större än vår ynkliga måne, som mäter bara cirka 2 160 mil. Men månen råkar också vara ca 400 gånger närmare jorden än solen (förhållandet varierar då båda omloppsbanorna är elliptiska), och som en följd av detta kan nymånen, när omloppsplanen skär och avstånden är gynnsamma, verka helt utplåna solens skiva. I genomsnitt inträffar en total solförmörkelse någonstans på jorden ungefär var 18:e månad. Det finns faktiskt två typer av skuggor: umbran är den del av skuggan där allt solljus är utstängt. Umbran tar formen av en mörk, slank kon. Den omges av penumbran, en ljusare, trattformad skugga från vilken solljuset delvis skyms. Under en total solförmörkelse kastar månen sin umbra på jordens yta; den skuggan kan svepa en tredjedel av vägen runt planeten på bara några timmar. De som har turen att vara placerade i umbrans direkta väg kommer att se solens skiva förminskas till en halvmåne när månens mörka skugga rusar mot dem över landskapet. Under den korta perioden av totalitet, då solen är helt täckt, uppenbaras den vackra koronan — solens svaga yttre atmosfär. Totaliteten kan pågå så länge som 7 minuter 31 sekunder, även om de flesta totala förmörkelser oftast är mycket kortare. Den 4 januari 2011 passerade månen framför solen i en partiell solförmörkelse - sett från delar av jorden. Här fångade den japanska och amerikanska satelliten samma hisnande händelse. Den unika vyn skapade vad som kallas en annulär solförmörkelse. Kreditera: Hinode/XRT Partiella solförmörkelser En partiell solförmörkelse uppstår när endast penumbran (den partiella skuggan) passerar över dig. I dessa fall förblir en del av solen alltid i sikte under solförmörkelsen. Hur stor del av solen som finns kvar beror på de specifika omständigheterna. Vanligen ger penumbran bara ett bländande slag mot vår planet över polartrakterna; i sådana fall kan platser långt borta från polerna men fortfarande inom penumbrans zon inte se mycket mer än en liten skans av solen dold av månen. I ett annat scenario kommer de som är placerade inom några tusen mil från vägen till en total solförmörkelse att se en partiell solförmörkelse. Ju närmare ni är totalitetens väg, desto större är solfördunklingen. Om du till exempel är placerad strax utanför den totala solförmörkelsens väg, kommer du att se solen avta till en smal halvmåne, och sedan tjockna upp igen när skuggan passerar förbi. Annular solförmörkelser En annulär förmörkelse, även om en sällsynt och fantastisk syn, är långt annorlunda än en total en. Himlen kommer att mörkna ... något; en sorts konstig “förfalskning skymning” eftersom så mycket av solen fortfarande visar. Den annulära solförmörkelsen är en underart till en partiell solförmörkelse, inte total. Den maximala varaktigheten för en annulär förmörkelse är 12 minuter 30 sekunder. En annulär solförmörkelse liknar dock en total solförmörkelse i och med att månen verkar passera centralt över solen. Skillnaden är att månen är för liten för att täcka solskivan helt. Eftersom månen kretsar runt jorden i en elliptisk bana kan dess avstånd från jorden variera från 221.457 kilometer till 252.712 kilometer. Men den mörka skuggkonen i månens umbra kan sträcka sig ut i inte längre än 235 700 kilometer; det är mindre än månens genomsnittliga avstånd från jorden. Så om månen befinner sig på något större avstånd når inte umbrans spets jorden. Under en sådan solförmörkelse når antumbran, en teoretisk fortsättning av umbran, marken, och vem som helst som befinner sig inom den kan se upp förbi endera sidan av umbran och se en annulus, eller ”ring av eld” runt månen. En bra analogi är att sätta en penny på en femcentare, med en penny som är månen, och en nickel som är solen. Hybridsolförmörkelser Dessa kallas också för annular-total (“A-T”) förmörkelser. Denna speciella typ av solförmörkelse inträffar när månens avstånd är nära sin gräns för att umbran ska nå jorden. I de flesta fall börjar en A-T-förmörkelse som en annulär solförmörkelse eftersom umbrans spets faller precis i brist på att få kontakt med Jorden; då blir den total, eftersom planetens rundhet når upp och snappar upp skuggspetsen nära mitten av vägen, sedan återvänder den slutligen till annular mot slutet av vägen. Eftersom månen verkar passera direkt framför solen kallas total-, annulär- och hybridförmörkelser också för ”centrala” förmörkelser för att skilja dem från förmörkelser som bara är partiella. Av alla solförmörkelser är omkring 28 procent totala; 35 procent är partiella; 32 procent annulära; och bara 5 procent är hybrider. Eklippar händer inte vid varje nymåne, förstås. Detta beror på att månens omloppsbana lutas drygt 5 grader i förhållande till jordens omloppsbana runt solen. Av denna anledning passerar månens skugga vanligen antingen över eller under jorden, varför en solförmörkelse inte inträffar. Men som regel, minst två gånger per år (och ibland så många som fem gånger på ett år), kommer en nymåne att anpassa sig på just ett sådant sätt att förmörka solen. Den punkten kallas för en nod. Beroende på hur nära nymånen närmar sig en nod avgör om en viss förmörkelse är central eller partiell. Och månens avstånd från jorden — och i mindre utsträckning jordens avstånd från solen — kommer naturligtvis att avgöra om en central förmörkelse är total, annulär eller en hybrid. Och dessa justeringar händer inte slumpmässigt, för efter ett visst tidsintervall kommer en förmörkelse att upprepa sig själv eller återvända. Detta intervall är känt som Saroscykeln och var känt så långt tillbaka som de tidiga kaldeiska astronomernas dagar för omkring 28 århundraden sedan. Ordet Saros betyder “repetition” och är lika med 18 år, 111⁄3 dagar (eller en dag mindre eller mer beroende på antalet skottår som har ingripit). Efter detta intervall är solens och månens relativa positioner i förhållande till en nod nästan desamma som tidigare. Den tredje dagen i intervallet gör att varje förmörkelse av en serie förskjuts i longitud en tredjedel av vägen runt Jorden i väster med avseende på dess föregångare. Den 29 mars 2006 svepte till exempel en total solförmörkelse över delar av västra och norra Afrika och sedan över södra Asien. En saros senare, den 8 april 2024, kommer denna förmörkelse att återkomma, utom i stället för Afrika och Asien, kommer den att spåra över norra Mexiko, centrala och östra USA och de maritima provinserna i Kanada. Man ska aldrig titta direkt på solen, men det finns sätt att säkert observera en solförmörkelse. Se hur man säkert observerar en solförmörkelse med denna Space.com infographic Credit: Karl Tate, SPACE.com Bidragsgivare När en solförmörkelse närmar sig, kommer de vanliga medierna ofta att ge en mängd varningar och råd mot att titta på solen med bara ögon, som blindhet kan uppstå. Detta har gett de flesta människor uppfattningen att solförmörkelser är farliga. Inte alls! Det är solen som är farlig — hela tiden! Solen avger ständigt osynliga infraröda strålar som kan skada dina ögon. Vanligtvis har vi ingen anledning att se på solen. En solförmörkelse ger oss en anledning, men vi bör inte. Det finns dock säkra sätt. . . Det säkraste sättet att se en solförmörkelse är att konstruera en ”pinhole-kamera”. Ett hål eller en liten öppning används för att bilda en bild av solen på en skärm som är placerad ca 3 fot (eller ca 1 meter) bakom öppningen. Kikare eller ett litet teleskop monterat på ett stativ kan också användas för att projicera en förstorad bild av solen på ett vitt kort. Ju längre bort kortet är, desto större kan du fokusera bilden. Leta efter solfläckar. Lägg märke till att solen verkar något mörkare runt extremiteten eller kanten. Denna metod för solskådning är säker så länge du inte kommer ihåg att inte titta genom kikaren eller teleskopet när de är riktade mot solen; uttryckt på ett annat sätt, aldrig titta direkt på solen när någon del av dess förblindande ljusa yta är synlig. En variant på pinholetemat är ”pinholespegeln”. Täck en fickspegel med ett papper som har ett 1⁄4-tums hål stansat i den. Öppna ett fönster som är vänt mot solen och placera den täckta spegeln på den solbelysta stollen så att den reflekterar en skiva med ljus på den bortre väggen inuti. Ljusskivan är en bild av solens ansikte. Ju längre bort från väggen desto bättre; bilden kommer att vara bara 1 tum tvärs över för varje 9 fot (eller 3 centimeter för varje 3 meter) från spegeln. Modellera lera fungerar bra för att hålla spegeln på plats. Experimentera med hål av olika storlek i pappret. Återigen gör ett stort hål bilden ljus, men suddig, och ett litet gör den dunkel men skarp. Mörka rummet så mycket som möjligt. Se till att prova detta i förväg för att se till att spegelns optiska kvalitet är tillräckligt bra för att projicera en ren, rund bild. Låt naturligtvis ingen se solen i spegeln. Om du är runt lövträd, titta på skuggan som kastas av dem under de partiella faserna. Vad ser du? Är det värt ett fotografi? Du kommer att se massor av delvis förmörkade solar projiceras genom hål gap mellan bladen. Detta orsakas av diffraktion, en egenskap av ljus. Enligt Vince Huegele, en optisk fysiker vid NASA Marshall Space Flight Center, skjuter ljusstrålarna inte rakt vid kanten av luckorna, eller ett hål, utan böjer sig runt kanten. Denna vågeffekt skapar ett mönster av ringar som påminner om ett tjuröga. Godtagbara filter för ohjälpliga visuella solobservationer inkluderar aluminiserade Mylar. En del astronomihandlare bär Mylarfiltermaterial som är speciellt utformat för solobservation. Också acceptabelt är skugga 14 bågsvetsglas, tillgänglig för bara några dollar i svetsförråd butiker. Naturligtvis är det alltid en bra idé att testa dina filter och / eller observera tekniker före solförmörkelse dag. Oacceptabla filter inkluderar solglasögon, gamla färgfilmsnegativ, svart-vit film som inte innehåller något silver, fotografiska neutral-densitetsfilter och polariserande filter. Även om dessa material har mycket låga nivåer av synlig ljustransmittans, överför de en oacceptabelt hög nivå av närinfraröd strålning som kan orsaka en termisk retinal brännskada. Det faktum att solen verkar svag eller att du inte känner något obehag när du tittar på solen genom dessa typer av filter, är ingen garanti för att dina ögon är säkra. Det finns en gång då man säkert kan titta direkt på solen: under en total solförmörkelse, då solens skiva är helt täckt. Under dessa få dyrbara sekunder eller minuter lyser den magnifika koronan fram i all sin härlighet kring den förmörkade solen; en underbar frans av pärlvitt ljus. Den skiljer sig i storlek, i färgtoner och mönster från förmörkelse till förmörkelse. Den är alltid svag och delikat, med ett sken som en blek aurora. Den har ett variabelt utseende. Ibland har den ett mjukt kontinuerligt utseende; vid andra tillfällen skjuter långa strålar av den ut i tre eller fyra riktningar. Den kan sticka ut från skivan i filmiga kronblad och streamers. Men när solen börjar komma fram igen, försvinner koronan snabbt och du måste skydda dina ögon igen. Detta foto av den partiella solförmörkelsen den 13 september 2015, knäpptes av astrofotografen K.J. Mulder från sitt hem i Sydafrika. Kredit: K.J. Mulder/Worlds på Bläck Så bra vi kan avgöra, det tidigaste rekordet av en solförmörkelse inträffade över fyra årtusenden sedan. I Kina trodde man att det gradvisa utplånandet av solen orsakades av en drake som försökte sluka solen, och det var hovastronomernas plikt att skjuta pilar, slå trummor och höja vilken kakofoni de än kunde skrämma bort draken. I den gamla kinesiska klassikern Shujing (eller Dokumentboken) finns berättelsen om Hsi och Ho, två hovastronomer som ertappades helt omedvetna av en solförmörkelse, efter att ha blivit berusad strax innan händelsen började. I efterdyningarna, Zhong Kang, beordrade Xiadynastins fjärde kejsare att Hsi och Ho skulle straffas genom att deras huvuden höggs av. Solförmörkelsen i fråga var den 22 oktober år 2134 f.Kr. I Bibeln, i Amos 8:9, står orden: ”Jag skall låta solen gå ner vid middagstid, och jag skall förmörka jorden på den klara dagen.” Bibliska forskare tror att detta är en hänvisning till en firad solförmörkelse som observerades i Nineve i det forntida Assyrien den 15 juni 763 f.Kr. En assyrisk tavla vittnar också om händelsen. En solförmörkelse stoppade till och med ett krig. Enligt historikern Herodotos pågick ett femårigt krig som rasade mellan lyderna och mederna. Då kriget skulle övergå i sitt sjätte år, en grekisk vise, förutsade Thales från Miletos för jonierna att den tid snart närmade sig då dagen skulle vända till natt. Den 17 maj 603 f.Kr. solen bleknade bort precis som Thales hade anspelat på att den skulle. I tron att det var ett tecken ovanifrån kallade de stridande för vapenvila, som befästes genom ett dubbeläktenskap, ty, som Herodotos skrev: "Utan något starkt band finns det inte mycket säkerhet i människornas förbund." Och att ge ordet "Rädd till döden" ny mening är den försagde kejsaren Ludvig av Bayern, Karl den stores son, som bevittnade en ovanligt lång total solförmörkelse den 5 maj år 840 e.Kr., som varade i över fem minuter. Men det dröjde inte länge förrän solen hade börjat gå upp igen, utan Ludvig blev så överväldigad av det han just hade sett att han dog av skräck! Astronomer har lärt sig mycket genom att studera solförmörkelser, och på 1700 - talet erkändes observationer av solförmörkelser ge veritabla skattkammare av astronomisk information, även om det ibland inte var lätt att få den informationen. Samuel Williams, professor vid Harvard, ledde en expedition till Penobscot Bay i Maine för att observera den totala solförmörkelsen 27 oktober 1780. Det visade sig att denna solförmörkelse ägde rum under revolutionskriget, och Penobscot Bay låg bakom fiendens linjer. Som tur var beviljade britterna expeditionen fri lejd, med hänvisning till vetenskapens intresse framför politiska meningsskiljaktigheter. Och ändå till slut var allt förgäves. Williams gjorde tydligen ett avgörande fel i sina beräkningar och placerade av misstag sina män vid Islesboro — strax utanför totalitetens väg — och fann detta med tungt hjärta, när den förträngningsrika månskäran av solljus helt gled runt månens mörka kant och sedan började tjockna! Under en total solförmörkelse kan några rubinröda fläckar tyckas sväva runt månens jetsvarta skiva. Det är solframträdanden, tungor av glödande vätegas som stiger upp över solens yta. Under den totala solförmörkelsen 18 augusti 1868 utbildade den franske astronomen Pierre Janssen sitt spektroskop på bemärktheterna och upptäckte ett nytt kemiskt grundämne. Två engelska astronomer, J. Norman Lockyer och Edward Frankland, döpte det senare till "helium", från grekiskans helios (solen). Gasen identifierades inte på jorden förrän 1895. Och eftersom solljuset blockeras under en total solförmörkelse, kan några av de ljusare stjärnorna och planeterna observeras på den förmörkade himlen. Under sådana förhållanden kunde astronomer testa en del av Einsteins nu celebrerade allmänna relativitetsteori. Den teorin förutspådde att ljus från stjärnor bortom solen skulle böja sig från en rak väg på ett visst sätt när den passerade solen. Stjärnornas positioner fotograferade nära solkanten under en total solförmörkelse den 29 maj 1919 jämfördes med fotografier av samma region på himlen tagna nattetid; resultaten stödde starkt Einsteins teori. Vår moderna teknik tillåter nu astronomer att göra de flesta av de observationer som en gång fick vänta på en solförmörkelse. Men en total solförmörkelse kommer alltid att förbli bland de mest imponerande av naturliga skådespel och är en syn som alltid kommer att bli ihågkommen. Var noga med att sätta upp det på din hink lista; du kommer inte att bli besviken. Om två år, den 21 augusti 2017, kommer nordamerikaner att få en möjlighet att observera naturens största skyshow. Föreställ dig detta: Dagen börjar ljus och solig. Sedan, lite senare, börjar du märka att, även om det fortfarande är soligt, dagen inte verkar riktigt så ljus. Och fortfarande ett litet tag senare, verkar det nästan som om en stor storm brygger. Sedan, plötsligt, och utan förvarning, midsommardagen blir konstigt mörkt. Några stjärnor kommer ut. Fåglar och djur blir förvirrade och beger sig snabbt hem för att sova. Nattinsekter börjar kvittra. Runt hela horisonten finns ett konstigt gulorange sken som liknar en konstig solnedgång. Och under tiden, uppe på himlen där solen ska vara, visas det istället en jetsvart skiva omgiven av en mjukt glödande gloria. [Förvånansvärt 2015 Solförmörkelsefoton] Då, lika plötsligt, lyser himlen upp. Stjärnorna försvinner, fåglar och djur vaknar, och solen återvänder. Vad ni just har bevittnat är en total solförmörkelse. Denna totala solförmörkelse 2017 kommer att vara första gången på nästan fyra decennier att en sådan händelse kommer att synas så nära hemmet. "Stäng", förstås, är en relativ term. Men för de flesta amerikaner kommer detta spektakulära fenomen att inträffa bokstavligt talat på deras egna bakgårdar. I motsats till vad folk tror är totalsolförmörkelser inte särskilt sällsynta. Astronomer förutspår att 68 kommer att äga rum under det nuvarande århundradet — ett som äger rum ungefär var 17,6: e månad. Vid sådana tillfällen kastar månen sin mörka, slanka kon av skugga (kallad umbran) över jordens yta. [How Solar Eclipses Work (Infographic)] Spåret som spåras av månens umbra kan köras i många tusen mil, men det är också mycket smalt – som mest, cirka 268 kilometer bred. Av denna anledning har man beräknat att en total solförmörkelse i genomsnitt är synlig från samma plats på jorden endast en gång på ungefär 375 år. På senare år har till exempel ihärdiga förmörkelsejägare varit tvungna att resa till avlägsna platser som Ellesmere Island i Nunavut, Kanada (2008), Påskön (2010) eller den norska ögruppen Svalbard (2015). Karta som visar vägen av totalitet över hela USA för den totala solförmörkelsen av augusti 21, 2017. Kredit: Fred Espenak/NASA GSFC Men 21 augusti 2017, kommer att markera första gången detta århundrade, och första gången sedan 1979, att en total solförmörkelse kommer att korsa sammanhängande (lägre 48) USA (Alaska hade sin tur 1990; Hawaii 1991). Och för allra första gången kommer skuggspåret — mer känt som "totalitetens väg" — att svepa endast över USA och inget annat land, vilket leder till att vissa människor kallar denna kommande händelse för "The Great American Eclipse". Många amerikaner som drar full nytta av denna händelses närhet till sina hem kommer att få ett gyllene tillfälle att själv bevittna en av de vackraste och mest spännande av naturens sky händelser. Den totala solförmörkelsen kommer att ses av uppskattningsvis 12 miljoner människor som turligt nog lever inom totalitetsbanan. Antalet personer som befinner sig inom bara en dags drivning av totalzonen är dock troligen runt 200 miljoner. [How to Safely Photograph the Sun (Photo Guide)] Inte sedan 1970 har det funnits en möjlighet att se en total solförmörkelse i så lättillgängliga och utbredda områden i USA. Det har funnits ett par begränsade möjligheter, som 1972 (Quebec och de angränsande kanadensiska maritima provinserna) och 1979 (the Pacific Northwest och Northern Plains), men siktområdena var antingen begränsade eller något svåra att nå. Och inte förrän april 2024 kommer det att finnas en annan möjlighet jämförbar med den som erbjuds den 21 augusti 2017. För första gången sedan 1918 kommer månens mörka skugga att svepa över USA från kust till kust. Vid den lokala soluppgången denna tredje måndag i augusti kommer månens skugga först att beröra jorden vid en punkt i norra Stilla havet, omkring 2.414 kilometer nordväst om Hawaiiöarna. Sedan, under 3 timmar och 13 minuter, kommer skuggan att rasa först öst-nordöst, sedan öst och slutligen sydost, längs vägen mörknar en smal remsa av den nordamerikanska kontinenten. Inledningsvis kommer skuggan bara korsa vidöppna havet i 28 minuter. Slutligen kommer det att göra landfall längs Oregons kust vid samhället Lincoln Beach. Den totala solförmörkelsen kommer att vara synlig inom en väg av mörker som sträcker sig från Oregon och sedan vidare genom Idaho, Wyoming, Nebraska, Kansas, Missouri, Illinois, Kentucky, Tennessee, Georgia, North Carolina och, slutligen, South Carolina. Stigen kommer i genomsnitt att vara 108 kilometer bred, men när den rör sig genom västra Kentucky, omkring 19 kilometer nordväst om staden Hopkinsville, kommer skuggans storlek att vidgas till högst 114 kilometer. Eftersom månens skugga rör sig med en sådan enorm hastighet kan totaliteten inte på något ställe vara särskilt länge. Den totala fasens varaktighet är alltid längst längs mitten av skuggans väg. När en observatör rör sig bort från centrum minskar totaltidens varaktighet och blir noll längs vägens kanter. [Video: How Total Solar Eclipse Photos Help Astronomers] Precis vid Oregons kust varar totaliteten 1 minut och 59 sekunder, eftersom skuggan kommer att färdas med mer än tre gånger ljudets hastighet (2 400 mph, eller 3 900 km/h). På väg åt sydost längs mittlinjen förlängs totaltiden långsamt och når högst 2 minuter och 40,3 sekunder vid en plats i södra Illinois omkring ett tiotal kilometer sydöst om staden Carbondale. Skuggan – som vid denna tidpunkt har avtagit till 1 450 mph (2,33 mil/h) – börjar sedan öka i hastighet, och totalitetens varaktighet börjar därefter minska. Ja, när den kommer till South Carolinas kustlinje, kommer totaltiden att ha sjunkit till 2 minuter och 34 sekunder. Skuggan går sedan ut till havs och lämnar slutligen jorden 75 minuter senare vid den lokala solnedgången i Nordatlanten, 627 kilometer sydväst om ön Kap Verde. Noterbara städer innanför totalitetsbanan är bland annat Idaho Falls, Idaho; Casper, Wyoming; Grand Island, Nebraska; Lincoln, Nebraska; Columbia, Missouri; Nashville, Tennessee; Columbia, South Carolina; och Charleston, South Carolina. Storstadsområdena Kansas City, Missouri och St Louis ligger precis vid kanten av totalitetsbanan. Varning: Stirra aldrig direkt på solen, vare sig med ditt öga utan hjälp eller genom teleskop och kikare, utan ordentligt skydd. Allvarliga ögonskador kan uppstå. Solförmörkelseobservatörer och astronomer använder speciella filter för att säkert observera solen. Väderexperter har genomfört studier för att hjälpa observatörer att välja bästa möjligheten för molnfri himmel i och nära vägen för totalitet den 21 augusti 2017. De bästa chanserna för ett tydligt utseende verkar finnas i området som löper från västra Oregon genom Wyoming, där i genomsnitt oddsen ligger på ungefär 70 procent. Går längre österut, minskar oddsen för klar himmel gradvis; från Kentucky till Atlantkusten, det är bara om ett mynt kasta för gynnsamt väder: bara 50-50. Med början veckan innan kommer National Weather Service att ge allt tillförlitligare prognoser, vilket kommer att göra det möjligt för människor att välja en plats där chanserna för en molnig himmel är låga. Omgivningen runt den mörka umbran är penumbran, eller partiell skugga. Den kommer också att vara konisk men mycket större — nästan 9700 kilometer i diameter. Penumbran är helt enkelt den halvskugga som ligger utanför varje djup skugga, vare sig den kastas av månen eller ett hus. Var penumbran än faller, kommer en partiell solförmörkelse att inträffa. Hela Nordamerika kommer att vara inne i penumbran, vilket orsakar en ganska stor partiell solförmörkelse för stora delar av USA och delar av sydvästra Kanada. Ju närmare du stationerar dig till totalitetens väg, desto större blir storleken på den partiella solförmörkelsen. När man tittar på de partiella faserna, bör man vara försiktig medan man betraktar den fortfarande förblindande ljusa solen. Ett antal stora städer kommer att ligga strax utanför totalzonen och kommer att se solen skäras ner till en ytterst tunn ljusstrimma. Dessa inkluderar Portland, Oregon, Omaha, Nebraska, Chattanooga, Tennessee och Atlanta. Från dessa städer kommer en underligt konstig skymningseffekt att falla ett par minuter. Men en partiell solförmörkelse bleknar i jämförelse med en total, även när 99 procent av solens skiva är skymd. Den stora föreställningen kan bara börja i det ögonblick då den sista solfläcken släcks. Och först när det är i total solförmörkelse är solen helt säker att titta på; endast inuti själva totalitetsbanan kan du bevittna förmörkelsens fulla storhet. Av den anledningen kommer många människor sannolikt att resa för att positionera sig inom vägen. Många av oss tar solen för given, och de tänker inte så mycket på den förrän den bränner vår hud eller kommer i våra ögon. Men vår stjärna är ett fascinerande och komplext objekt, en gigantisk fusionsreaktor som ger oss liv. Hur mycket vet du om solen? Starta testet 0 av 10 frågor komplett Solar Quiz: Hur väl känner du vår sol? Många av oss tar solen för given, och de tänker inte så mycket på den förrän den bränner vår hud eller kommer i våra ögon. Men vår stjärna är ett fascinerande och komplext objekt, en gigantisk fusionsreaktor som ger oss liv. Hur mycket vet du om solen? 0 av frågorna klara Utan tvekan, kommer "All American Eclipse" att vara en av de stora nyheterna 2017. De stora nyhetsnätverken kommer säkert att distribuera grupper av kameror och reportrar längs hela vägen och kommer att följa månens umbra under dess 90-minuters svep över det sammanhängande USA. Mediebevakning – åtminstone för denna en dag – kan påminna om den täckning som åtföljer de första flygningarna med rymdfärjan. Kort sagt, den tredje måndagen i augusti 2017 kommer att bli en fantastisk dag. Markera era kalendrar! 2017 EFFEKTIV WEBBPLATSER: http://eclipse.gsfc.nasa.gov/SEgoogle/SEgoogle2001/SE2017Aug21Tgoogle.html http://www.greatamericaneclipse.com/eclipse-2017/ http://www.eclipse2017.org/2017/path_through_the_US.htm http://aa.usno.navy.mil/data/docs/Eclipse2017.php http://www.shadowandposic.com/2017/2017/2017e.html Redaktörens anmärkning: Om du har ett foto med skyskådning som du vill dela för en möjlig berättelse eller bildgalleri, skicka bilder och kommentarer till Space.com på spacephotos@space.com. Joe Rao tjänstgör som instruktör och gästföreläsare vid New Yorks Hayden Planetarium. Han skriver om astronomi för tidskriften Natural History, Farmer's Almanac och andra publikationer, och han är även meteorolog på kameran för News 12 Westchester, New York.Följ oss @Spacedotcom, Facebook och Google+. Originalartikel på Space.com. Öh Washington, 22 augusti (UPI) -- Markera dina kalendrar för 21 augusti 2017. Det är då hela Nordamerika får en glimt en gång i livet av en total solförmörkelse. Den stora amerikanska eclipsen, som den har dubbats till, kommer för första gången på närmare fyra årtionden att bli synlig för miljoner människor i hela USA. Det kommer att markera första gången detta århundrade en total solförmörkelse kommer att passera genom det sammanhängande USA. Det är också första gången skuggspåret, som kallas totalitetens väg, sveper över USA och inget annat land. Omkring 200 miljoner människor kommer att kunna nå solförmörkelsens väg, som kommer att svepa nationen från South Carolina till Oregon, inom en dags bilresa. Tjänstemän i Hopkinsville, Ky., kallar det den största händelsen att slå till mot staden på 32 000. Staden kommer att uppleva den längsta perioden av totalitet någon stad på 2 minuter och 40 sekunder. Stadsledare räknar med att upp till 50.000 besökare kommer att föra in omkring 23,6 miljoner dollar i området. De presenterade nyligen stadens logotyp för evenemanget och planerar för dagar långa festligheter. "Det är en unik möjlighet och det är vår stora ursäkt att rulla ut den röda mattan och vara den bästa versionen av Hopkinsville vi kan vara", sade borgmästare Carter Hendricks. "Vetenskapen har gett oss den bästa visningsplatsen strax norr om Hopkinsville. Det är upp till oss att främja ordentligt så att folk vill komma och vara här." Skriv en sammanfattning.
A total eclipse is unlike anything you've seen in your life. As totality approaches, you will see the amazing sight of day turning into night and the coronas of the sun blaze in the sky. This is indeed a great American solar eclipse because totality will sweep the nation from the Pacific to the Atlantic Ocean. Almost everyone in the United States can reach this total solar eclipse within a day's operation. A solar eclipse is a cosmic billiard shot—the sun, moon, and earth are lined up to reveal the sun's atmosphere, it's corona. Eclipses on earth occur only because of a marvelous heavenly coincidence. Editor's note: The Great American Solar Eclipse was August 21, 2017. It swept across the continental United States from Oregon to Georgia. See our full coverage. Another total solar eclipse will be seen across the United States in 2024. A solar eclipse occurs when the moon comes between the earth and the sun, and the moon casts a shadow over the earth. A solar eclipse can only occur at the phase of the new moon, when the moon passes directly between the sun and the earth and its shadows fall on the surface of the earth. However, whether the adjustment gives rise to a total solar eclipse, a partial solar eclipse or an annular solar eclipse is due to several factors, all explained below. That an eclipse can occur at all is a fluke of celestial mechanics and time. Since the moon was formed some 4.5 billion years ago, it has been gradually moved away from the earth (about 1.6 inches, or 4 centimeters per year). Right now the moon is at the perfect distance to appear in our sky exactly as large as the sun, and therefore block it. But this is not always true. The next solar eclipse is a partial solar eclipse that will take place on January 5–6, 2019. It will be visible from northeastern Asia, the Pacific Ocean and parts of Alaska. A total solar eclipse will occur on July 2, 2019, in South America. To find out about upcoming solar eclipses and how to see them, check our guide. How solar eclipses work: When the moon covers the sun, skywatchers rejoice at the possibility of seeing a rare spectacle. See how solar eclipses occur in this Space.com infographic Credit: Karl Tate, SPACE.com Contributors There are four types of solar eclipses: total, annular, partial and hybrid. Here is what causes each type: Total solar eclipses These are a happy accident of nature. The diameter of the sun of 864,000 miles [864,000 km] is 400 times that of our puny moon, measuring only about 2,600 miles [2,600 km]. But the moon also happens to be about 400 times closer to the earth than the sun (the ratio varies as both orbits are elliptical), and as a result, when the orbital plane intersects and distances are favorable, the new moon may seem to completely obliterate the sun's disk. On average, a total eclipse occurs somewhere on earth approximately every 18 months. There are actually two types of shadows: the umbra is the part of the shadow where all sunlight is shut out. Umbran takes the form of a dark, slender cow. It is surrounded by the penumbra, a lighter, funnel-shaped shadow from which sunlight is partially obscured. During a total eclipse, the moon throws its umbra on the surface of the earth; that shadow can sweep a third of the road around the planet in just a few hours. Those lucky enough to be placed in the direct path of the umbra will see the sun's disk reduced to a crescent moon as the moon's dark shadow rushes toward them across the landscape. During the short period of totality, when the sun is fully covered, the beautiful corona — the sun’s faint outer atmosphere is revealed. Totality can last as long as 7 minutes 31 seconds, although most total eclipses are usually much shorter. On January 4, 2011, the moon passed in front of the sun in a partial eclipse - seen from parts of the earth. Here the Japanese and American satellites captured the same breathtaking event. The unique view created what is called an annular eclipse. Credit: Hinode/XRT Partial solar eclipses A partial solar eclipse occurs when only the penumbra (the partial shadow) passes over you. In these cases, part of the sun always remains in sight during the eclipse. How much of the sun remains depends on the specific circumstances. Usually, the penumbra only gives a dazzling blow to our planet across the polar regions; in such cases, places far away from the poles but still within the penumbra's zone may not see much more than a small scan of the sun hidden by the moon. In another scenario, those located within a few thousand miles of the road to a total eclipse will see a partial eclipse. The closer you are to the path of totality, the greater the sun obscurity. For example, if you are located just outside the path of total eclipse, you will see the sun waning to a narrow crescent, then thickening up again as the shadow passes by. Annular solar eclipses An annular eclipse, although a rare and amazing sight, is far different from a total one. The sky will darken ... slightly; a kind of strange “forgery twilight” because so much of the sun still shows. The annular eclipse is a subspecies of a partial eclipse, not total. The maximum duration of an annular eclipse is 12 minutes 30 seconds. However, an annular solar eclipse resembles a total solar eclipse with the moon appearing to pass centrally over the sun. The difference is that the moon is too small to cover the solar disk completely. As the moon orbits the earth in an elliptical orbit, its distance from the earth can range from 221,457 miles to 252,712 miles (252,712 kilometers). But the dark shadow cone in the umbra of the moon can extend for no longer than 2,35,700 kilometers; it is less than the average distance of the moon from the earth. So if the moon is at any greater distance, the tip of the umbra does not reach the Earth. During such an eclipse, the antumbran, a theoretical continuation of the umbran, reaches the ground, and anyone within it can look up past either side of the umbran and see an annulus, or “ring of fire” around the moon. A good analogy is to put a penny on a nickel, with a penny that is the moon, and a nickel that is the sun. Hybrid solar eclipses These are also called annular-total (“A-T”) eclipses. This particular type of solar eclipse occurs when the moon's distance is near its limit for the umbre to reach the Earth. In most cases, an A-T eclipse begins as an annular solar eclipse because the tip of the umbre falls just for lack of contact with Earth; then it becomes total, as the roundness of the planet reaches up and intercepts the shadow tip near the middle of the road, then finally returns to the annular towards the end of the road. Because the moon appears to pass directly in front of the sun, total, annular and hybrid eclipses are also called “central” eclipses to distinguish them from eclipses that are only partial. Of all solar eclipses, about 28 percent are total; 35 percent are partial; 32 percent are annular; and only 5 percent are hybrids. Ecuts don't happen at every new moon, of course. This is because the moon's orbit is tilted just over 5 degrees in relation to the earth's orbit around the sun. For this reason, the shadow of the moon usually passes either above or below the earth, so an eclipse does not occur. But as a rule, at least twice a year (and sometimes as many as five times in a year), a new moon will adapt in just such a way as to darken the sun. That point is called a node. Depending on how close the new moon approaches a node determines whether a certain eclipse is central or partial. And the distance of the moon from the earth — and to a lesser extent the distance of the earth from the sun — will, of course, determine whether a central eclipse is total, annular, or hybrid. And these adjustments do not happen randomly, for after a certain time interval an eclipse will repeat itself or return. This interval is known as the Saros Cycle and was known as far back as the days of the early Chaldean astronomers some 28 centuries ago. The word Saros means “repetition” and is equal to 18 years, 111⁄3 days (or one day less or more depending on the number of leap years that have intervened). After this interval, the relative positions of the sun and moon relative to a node are almost the same as before. On the third day of the interval, each eclipse of a series is displaced in longitude one third of the road around the Earth in the west with respect to its predecessors. For example, on March 29, 2006, a total solar eclipse swept over parts of western and northern Africa and then across southern Asia. A saros later, on April 8, 2024, this eclipse will return, except in place of Africa and Asia, it will track across northern Mexico, the central and eastern United States and the maritime provinces of Canada. You should never look directly at the sun, but there are ways to observe a solar eclipse safely. See how to safely observe a solar eclipse with this Space.com infographic Credit: Karl Tate, SPACE.com Contributor When a solar eclipse approaches, the usual media will often give a variety of warnings and advice against looking at the sun with just eyes, as blindness may occur. This has given most people the view that eclipses are dangerous. Not at all! It is the sun that is dangerous — all the time! The sun is constantly emitting invisible infrared rays that can damage your eyes. Usually we have no reason to look at the sun. A solar eclipse gives us a reason, but we shouldn't. However, there are certain ways. . . . . . . The safest way to see an eclipse is to construct a pinhole camera. A hole or a small opening is used to form an image of the sun on a screen that is placed about 3 feet (or about 1 meter) behind the opening. Binoculars or a small telescope mounted on a stand can also be used to project an enlarged image of the sun on a white card. The further away the card, the bigger you can focus the image. Look for sunspots. Notice that the sun seems somewhat darker around the limb or edge. This method of sun viewing is safe as long as you do not remember not looking through the binoculars or telescope when they are directed at the sun; expressed in another way, never look directly at the sun when any part of its blinding bright surface is visible. One variant of the pinhole theme is the ‘pinhole mirror’. Cover a pocket mirror with a paper that has a 1⁄4-inch hole punched in it. Open a window facing the sun and place the covered mirror on the sunlit fool so that it reflects a disk with light on the far wall inside. The light disc is a picture of the face of the sun. The further away from the wall, the better; the picture will be just 1 inch across for each 9 feet (or 3 centimetres for each 3 meters) from the mirror. Modeling clay works well to keep the mirror in place. Experiment with holes of different sizes in the paper. Again, a large hole makes the image bright, but blurred, and a small one makes it dim but sharp. Dark room as much as possible. Make sure to try this in advance to make sure the optical quality of the mirror is good enough to project a clean, round image. Of course, let no one see the sun in the mirror. If you are around deciduous trees, look at the shadow thrown by them during the partial phases. What do you see? Is it worth a photograph? You will see lots of partially darkened suns projected through holes gap between the leaves. This is caused by diffraction, a characteristic of light. According to Vince Huegele, an optical physicist at NASA Marshall Space Flight Center, the light rays do not shoot straight at the edge of the hatches, or a hole, but bend around the edge. This wave effect creates a pattern of rings resembling a bull’s eye. Acceptable filters for unhelpful visual solar observations include aluminized Mylar. Some astronomers carry Mylar filter materials specially designed for solar observation. Also acceptable is shadow 14 arc welding glass, available for just a few dollars in welding stores. Of course, it is always a good idea to test your filters and/or observe techniques before solar eclipse day. Unacceptable filters include sunglasses, old color film negative, black-white film containing no silver, photographic neutral-density filters and polarizing filters. Although these materials have very low levels of visible light transmittance, they transmit an unacceptably high level of near-infrared radiation that can cause a thermal retinal burn. The fact that the sun seems weak or that you feel no discomfort when looking at the sun through these types of filters, is no guarantee that your eyes are safe. There is one time when you can surely look directly at the sun: during a total eclipse, when the sun's disc is completely covered. During these few precious seconds or minutes, the magnificent corona shines forth in all its glory around the darkened sun; a wonderful fringe of pearly white light. It differs in size, in hues and patterns from eclipse to eclipse. It is always weak and delicate, with a glow like a pale aurora. It has a variable appearance. Sometimes it has a soft continuous appearance; at other times long rays of it shoot out in three or four directions. It can stand out from the record in filmy petals and streamers. But when the sun starts to come out again, the corona disappears quickly and you have to protect your eyes again. This photo of the partial solar eclipse on September 13, 2015, was snapped by astrophotographer K.J. Mulder from his home in South Africa. Credit: K.J. Mulder/Worlds on Ink As best we can tell, the earliest record of a solar eclipse occurred over four millennia ago. In China, it was believed that the gradual extinction of the sun was caused by a dragon trying to devour the sun, and it was the duty of the court astronomers to shoot arrows, beat drums, and raise whatever cacophony they could scare the dragon away. In the old Chinese classic Shujing (or the Book of Documents), there is the story of Hsi and Ho, two court astronomers who were caught completely unconscious by a solar eclipse, after getting drunk just before the event began. In the aftermath, Zhong Kang, the fourth emperor of the Xia dynasty ordered Hsi and Ho to be punished by cutting off their heads. The eclipse in question was October 22, 2134 BC. The Bible, in Amos 8:9, says: “I will set the sun at noon, and I will darken the earth on the clear day.” Biblical scholars believe that this is a reference to a celebrated eclipse observed in Nineveh in ancient Assyria on June 15, 763 BC. An Assyrian tablet also testifies to the incident. A solar eclipse even stopped a war. According to historian Herodotus, there was a five-year war raging between the obeyers and the Medes. As the war was about to pass in its sixth year, a Greek sage, Thales of Miletus foretold to the Ionians that the time was soon approaching when the day would turn to night. 17 May 603 BC. The sun faded away just as Thales had alluded to it. In the belief that it was a sign from above, the fighters called a truce, which was consolidated by a double marriage, for, as Herodotus wrote: "Without any strong bond there is little security in the covenant of men." And to give the word "Save to Death" new meaning is the timid emperor Louis of Bavaria, Charlemagne's son, who witnessed an unusually long total eclipse of the sun on May 5, 840 AD, which lasted over five minutes. Before long, however, the sun had begun to rise again, but Louis was so overwhelmed by what he had just seen that he died of terror! Astronomers have learned much from studying eclipses, and in the 18th century observations of eclipses were recognized as providing veritable treasuries of astronomical information, although it was sometimes not easy to obtain that information. Samuel Williams, professor at Harvard, led an expedition to Penobscot Bay, Maine, to observe the total eclipse of October 27, 1780. It turned out that this eclipse took place during the Revolutionary War, and Penobscot Bay was behind enemy lines. Fortunately, the British granted the expedition safe passage, citing the interest of science over political differences. And yet, in the end, everything was in vain. Apparently Williams made a decisive error in his calculations and accidentally placed his men at Islesboro — just outside the path of totality — and found this with a heavy heart when the narrowing moon’s crescent of sunlight completely slid around the dark edge of the moon and then began to thicken! During a total eclipse, some ruby - red spots may seem to hover around the moon’s jet - black disc. It is solar appearances, tongues of glowing hydrogen gas rising above the surface of the sun. During the total solar eclipse of August 18, 1868, French astronomer Pierre Janssen trained his spectroscope on the prominences and discovered a new chemical element. Two English astronomers, J. Norman Lockyer and Edward Frankland, later named it "helium", from the Greek helios (the sun). The gas was not identified on Earth until 1895. And since sunlight is blocked during a total eclipse, some of the brighter stars and planets can be observed in the darkened sky. Under such conditions, astronomers were able to test some of Einstein's now-celebrated general theory of relativity. That theory predicted that light from stars beyond the sun would bend from a straight path in a certain way as it passed the sun. The positions of the stars photographed near the edge of the sun during a total eclipse on 29 May 1919 were compared to photographs of the same region in the sky taken at night; the results strongly supported Einstein's theory. Our modern technology now allows astronomers to make most of the observations that once had to wait for an eclipse. But a total eclipse will always remain among the most impressive of natural spectacles and is a sight that will always be remembered. Be sure to put it on your bucket list; you will not be disappointed. In two years, on August 21, 2017, North Americans will have an opportunity to observe nature's greatest sky show. Imagine this: The day begins bright and sunny. Then, a little later, you begin to notice that, although it is still sunny, the day does not seem quite so bright. And still a little while later, it seems like a big storm is brewing. Then, suddenly, and without warning, Midsummer Day gets strangely dark. Some stars are coming out. Birds and animals become confused and quickly go home to sleep. Night insects are starting to chirp. Around the whole horizon is a strange yellow-orange glow that resembles a strange sunset. And in the meantime, up in the sky where the sun should be, there is shown instead a jet black disc surrounded by a softly glowing halo. [surprisingly 2015 Solar eclipse photos] Then, just as suddenly, the sky lights up. The stars disappear, birds and animals wake up, and the sun returns. What you've just witnessed is a total eclipse. This total solar eclipse in 2017 will be the first time in nearly four decades that such an event will appear so close to home. "Close," of course, is a relative term. But for most Americans, this spectacular phenomenon will occur literally in their own backyards. Contrary to popular belief, total solar eclipses are not very rare. Astronomers predict that 68 will take place in the present century — one that takes place approximately every 17.6 months. At such times the moon throws its dark, slender cone of shadow (called the umbran) over the surface of the earth. [How Solar Eclipses Work (Infographic)] The track tracked by the moon's umbra can run for many thousands of miles, but it is also very narrow – at most, about 268 kilometers wide. For this reason it has been estimated that a total eclipse is visible on average from the same place on earth only once in about 375 years. For example, in recent years persistent eclipse hunters have had to travel to remote places such as Ellesmere Island in Nunavut, Canada (2008), Easter Island (2010) or the Norwegian archipelago of Svalbard (2015). Map showing the way of totality across the United States for the total eclipse of August 21, 2017. Credit: Fred Espenak/NASA CSDC But August 21, 2017, will mark the first time this century, and the first time since 1979, that a total eclipse will cross contiguous (lower 48) United States (Alaska had its turn in 1990; Hawaii 1991). And for the very first time, the shadow trail — better known as the "way of totality" — will sweep only across the United States and no other country, leading some people to call this upcoming event "The Great American Eclipse". Many Americans who take full advantage of the proximity of this event to their homes will have a golden opportunity to witness for themselves one of the most beautiful and exciting of nature's sky events. The total eclipse will be seen by an estimated 12 million people who fortunately live within the totality path. However, the number of people within just one day of drifting the total zone is probably around 200 million. [How to Safely Photograph the Sun (Photo Guide)] Not since 1970 has there been an opportunity to see a total solar eclipse in such easily accessible and widespread areas of the United States. There have been a couple of limited opportunities, such as in 1972 (Quebec and the neighboring Canadian maritime provinces) and 1979 (the Pacific Northwest and Northern Plains), but the sighting areas were either limited or somewhat difficult to reach. And not until April 2024 will there be another possibility comparable to that offered on August 21, 2017. For the first time since 1918, the dark shadow of the moon will sweep across the United States from coast to coast. At the local sunrise on this third Monday of August, the shadow of the moon will first touch the earth at a point in the northern Pacific Ocean, about 2,114 miles (2,414 km) northwest of the Hawaiian Islands. Then, for 3 hours and 13 minutes, the shadow will collapse first east-northeast, then east and finally southeast, along the road darkening a narrow strip of the North American continent. Initially, the shadow will only cross the wide open sea for 28 minutes. Finally, it will make landfall along the coast of Oregon on the community of Lincoln Beach. The total eclipse will be visible within a path of darkness extending from Oregon and then further through Idaho, Wyoming, Nebraska, Kansas, Missouri, Illinois, Kentucky, Tennessee, Georgia, North Carolina and, finally, South Carolina. The path will average 10 miles (108 km) wide, but as it moves through western Kentucky, about 20 miles (19 km) northwest of the city of Hopkinsville, the size of the shadow will widen to a maximum of 11 miles (114 km). As the shadow of the moon moves at such a huge speed, totality cannot be in any place very long. The duration of the total phase is always the longest along the middle of the path of the shadow. When an observer moves away from the center, the duration of the total time decreases and becomes zero along the edges of the road. [Video: How Total Solar Eclipse Photos Help Astronomers] Right on the coast of Oregon, the totality lasts 1 minute and 59 seconds, as the shadow will travel at more than three times the speed of sound (2,400 mph, or 3,900 km/h). Heading southeast along the midline, total time is slowly extended reaching a maximum of 2 minutes and 40.3 seconds at a location in southern Illinois about ten kilometres southeast of the town of Carbondale. The shadow – which at this point has slowed to 1,450 mph (2.33 miles/h) – then begins to increase in speed, and the duration of totality subsequently begins to decline. Yes, by the time it gets to the South Carolina coastline, total time will have dropped to 2 minutes and 34 seconds. The shadow then goes out to sea and finally leaves the earth 75 minutes later at the local sunset in the North Atlantic, 627 kilometers southwest of the island of Cape Verde. Notable cities inside the totality track include Idaho Falls, Idaho; Casper, Wyoming; Grand Island, Nebraska; Lincoln, Nebraska; Columbia, Missouri; Nashville, Tennessee; Columbia, South Carolina; and Charleston, South Carolina. The metropolitan areas of Kansas City, Missouri and St. Louis are located right on the edge of the totality track. Warning: Never stare directly at the sun, whether with your eye without help or through telescopes and binoculars, without proper protection. Serious eye damage may occur. Solar eclipse observers and astronomers use special filters to safely observe the sun. Weather experts have conducted studies to help observers choose the best opportunity for cloud-free skies in and near the path of totality on 21 August 2017. The best chances for a clear appearance appear to be in the area running from western Oregon through Wyoming, where average odds are about 70 percent. Going further east, the odds of clear skies are gradually decreasing; from Kentucky to the Atlantic coast, it's only about a coin throwing for favorable weather: only 50-50. Starting the week before, the National Weather Service will provide ever more reliable forecasts, which will allow people to choose a place where chances for a cloudy sky are low. The surrounding area around the dark umbra is the penumbra, or partial shadow. It will also be conical but much larger — nearly 2,700 kilometers in diameter. The penumbra is simply the half shadow that lies outside every deep shadow, whether thrown by the moon or a house. Wherever the penumbra falls, a partial eclipse will occur. The whole of North America will be inside the penumbra, causing a fairly large partial solar eclipse for much of the United States and parts of southwestern Canada. The closer you station yourself to the path of totality, the greater the size of the partial eclipse. When looking at the partial phases, caution should be exercised while viewing the still blinding bright sun. A number of large cities will be located just outside the total zone and will see the sun cut down to an extremely thin light streak. These include Portland, Oregon, Omaha, Nebraska, Chattanooga, Tennessee and Atlanta. From these cities, a strangely strange twilight effect will fall for a few minutes. But a partial eclipse fades in comparison to a total, even when 99 percent of the sun’s disk is obscured. The great performance can only begin at the moment when the last sunspot is extinguished. And only when it is in total solar eclipse is the sun absolutely certain to look at; only within the orbit of totality itself can you witness the full greatness of the eclipse. For this reason, many people are likely to travel to position themselves within the road. Many of us take the sun for granted, and they do not think much about it until it burns our skin or comes into our eyes. But our star is a fascinating and complex object, a gigantic fusion reactor that gives us life. How much do you know about the sun? Start the test 0 out of 10 questions complete Solar Quiz: How well do you know our sun? Many of us take the sun for granted, and they do not think much about it until it burns our skin or comes into our eyes. But our star is a fascinating and complex object, a gigantic fusion reactor that gives us life. How much do you know about the sun? 0 of the questions clear Without a doubt, "All American Eclipse" will be one of the major news in 2017. The major news networks will certainly distribute groups of cameras and reporters all along the way and will follow the moon's umbra during its 90-minute sweep across the contiguous United States. Media coverage – at least for this one day – may recall the coverage accompanying the first flights with the space shuttle. In short, the third Monday in August 2017 will be a great day. Mark your calendars! 2017 EFFECT WEBSITES: http://eclipse.gsfc.nasa.gov/SEgoogle/SEgoogle2001/SE2017Aug21Tgoogle.html http://www.greatamericaneclipse.com/eclipse-2017/ http://www.eclipse2017.org/2017/path_through_the_US.htm http://aa.usno.navy.mil/data/docs/Eclipse2017.php http://www.shadowandposic.com/2017/2017/2017/2017e.html Editor's note: If you have a photo with skywatching that you want to share for a possible story or image gallery, send images and comments to Space.com at spacephotos@space.com. Joe Rao serves as an instructor and guest lecturer at New York's Hayden Planetarium. He writes about astronomy for the journal Natural History, Farmer's Almanac and other publications, and he is also a meteorologist on the camera for News 12 Westchester, New York.Follow us @Spacedotcom, Facebook and Google+. Original article at Space.com. Uh Washington, August 22 (UPI) -- Select your calendars for August 21, 2017. That's when the whole of North America gets a glimpse once in a lifetime of a total eclipse. The great American eclipse, to which it has been dubbed, will for the first time in nearly four decades become visible to millions of people throughout the United States. It will mark the first time this century a total solar eclipse will pass through the contiguous United States. It is also the first time the shadow trail, known as the path of totality, sweeps across the United States and no other country. Some 200 million people will be able to reach the path of the eclipse, which will sweep the nation from South Carolina to Oregon, within a day’s drive. Officials in Hopkinsville, Ky., call it the biggest event to strike the city at 32,000. The city will experience the longest period of totality any city in 2 minutes and 40 seconds. City leaders expect that up to 50,000 visitors will bring about $23.6 million into the area. They recently presented the city logo for the event and plan for days of festivities. "It's a unique opportunity and it's our big excuse to roll out the red carpet and be the best version of Hopkinsville we can be," said Mayor Carter Hendricks. "Science has given us the best screening spot just north of Hopkinsville. It's up to us to promote properly so that people want to come and be here." Write a summary.
– Har du någonsin drömt om att se himlen mörkna och stjärnorna blinka mitt på en sommardag? Markera sedan din kalender för augusti 21, 2017, eftersom om du är i USA är chanserna goda att du kommer att vara bland de 200 miljoner eller så människor inom en dags drift av landets första totala solförmörkelse sedan 1979, rapporterar Space.com. Medan totala solförmörkelser är vanligare än många inser, med 68 detta århundrade, kommer denna förmörkelse att vara den första sedan 1918 där månens skugga – den så kallade "totalitetens väg" – kommer att svepa över USA från kust till kust. Den kallas den stora amerikanska eclipsen eftersom den kommer att synas från inget annat land på planeten. Totala solförmörkelser är tekniskt sett "en fluke av himmelsk mekanik och tid", tillägger Space.com, eftersom just nu månen, som gradvis rör sig bort från jorden, råkar vara det perfekta avståndet för att synas lika stort som solen. Månens skugga kommer att helt blockera solen under den längsta varaktigheten, två minuter och 40 sekunder, strax utanför Hopkinsville, Ky., och hyllas som den största händelsen att någonsin träffa staden med 32 000 människor, rapporterar UPI. Men den bästa insatsen för tydlig visning sägs vara i Oregon, där totaliteten bara kommer att räcka 2 minuter men det finns en 70% chans till klar himmel, i motsats till bara 50% från Kentucky österut genom South Carolina. Den väg av totalitet kommer att genomsnitt 67 miles i bredd, med några anmärkningsvärda städer i sin väg, inklusive Lincoln, Neb., Columbia, Mo., och Nashville, Tenn. För dem utanför vägen för totalitet men i den kontinentala USA, en partiell solförmörkelse bör fortfarande vara synlig, även om himlen kommer att vara betydligt mindre mörk. (Den senaste totala solförmörkelsen var i mars.)
– Have you ever dreamed of seeing the sky darkened and the stars flash in the middle of a summer day? Then mark your calendar for August 21, 2017, because if you are in the United States, chances are good that you will be among the 200 million or so people within a day's operation of the country's first total solar eclipse since 1979, reports Space.com. While total solar eclipses are more common than many realize, with 68 this century, this eclipse will be the first since 1918 where the shadow of the moon—the so-called "way of totality"—will sweep across the United States from coast to coast. It is called the Great American Eclipse because it will be visible from no other country on the planet. Total solar eclipses are technically "a fluke of heavenly mechanics and time," adds Space.com, because right now the moon, which is gradually moving away from the earth, happens to be the perfect distance to appear as large as the sun. The moon's shadow will completely block the sun for the longest duration, two minutes and 40 seconds, just outside Hopkinsville, Ky., and is hailed as the greatest event to ever hit the city with 32,000 people, reports UPI. But the best bet for clear display is said to be in Oregon, where the totality will only last 2 minutes but there is a 70% chance of clear sky, as opposed to just 50% from Kentucky east through South Carolina. The path of totality will average 67 miles in width, with some notable cities in its path, including Lincoln, Neb., Columbia, Mo., and Nashville, Tenn. For those off the road of totality but in the continental United States, a partial eclipse should still be visible, although the sky will be considerably less dark. (The last total eclipse was in March.)