A mountain-size space rock cruised past Earth this morning (Sept. 1) in a record-breaking encounter that has long had scientists drooling.

At 8:06 a.m. EDT (1206 GMT) today, the roughly 2.7-mile-wide (4.4 kilometers) asteroid 3122 Florence came within a mere 4.4 million miles (7 million km) of Earth — just 18 times the distance from our planet to the moon.

"Nothing this big has passed this close to Earth since we've been tracking," Paul Chodas, manager of the Center for Near-Earth Object Studies at NASA's Jet Propulsion Laboratory in Pasadena, California, told Space.com. "This is a once-in-40-year-event kind of thing." [Famous Asteroid Rock Flybys and Close Calls (Infographic)]

The big asteroid 3122 Florence, as seen by the Virtual Telescope Project on Aug. 30, 2017 — two days before its closest approach to Earth. (Image credit: Gianluca Masi/Virtual Telescope Project)

Only 10 or so asteroids as big as Florence exist in near-Earth space, Chodas said. There was never any chance of the space rock hitting us on this encounter, and astronomers have mapped out Florence's orbit well enough to know that it poses no threat to Earth for the next few centuries at least, he stressed. (But if something as big as Florence did hit us, it would be very bad: Scientists regard any impactor at least 0.6 miles, or 1 km, across as a potential civilization-ender.)

Florence was discovered by astronomer Schelte "Bobby" Bus in 1981 at Australia's Siding Spring Observatory. The space rock loops around the sun every 2.35 years on an elliptical path, getting as close to our star as 1 astronomical unit (AU) and as far away as 2.5 AU. (One AU is the average Earth-sun distance — about 93 million miles, or 150 million km.)

Astronomers have also determined that Florence is a superfast spinner, completing one rotation every 2.4 hours.

"If it were spinning any faster, it would fly apart," Chodas said. "What often happens is, asteroids that are spinning this quickly rearrange into the shape of a top, where they have kind of a bulge at the equator."

But that's just an inference in Florence's case; the asteroid's shape isn't known for certain. Indeed, not much about Florence is. For example, astronomers don't know if the space rock has a moon. And the 2.7-mile size estimate, which is based on infrared observations by NASA's Spitzer Space Telescope and NEOWISE mission, is just that — an estimate. It could change once researchers get some better observations, Chodas said.

"There's a lot to learn about this little world," he said.

On Sept. 1, asteroid Florence will fly by Earth, and come to within about 18 times the distance from the Earth to the moon. (Image credit: NASA)

Which brings us back to today's flyby. Florence has come close enough on this encounter — eight times closer to Earth than it's ever been since its 1981 discovery, Chodas said — to be pinged by radar, and scientists are taking full advantage of the opportunity. They've been using powerful facilities such as NASA's Goldstone Solar System Radar in California and the Arecibo Observatory in Puerto Rico to get the first-ever good looks at Florence.

The radar images should reveal Florence's true size and shape. They may even achieve 10-foot (3 meters) resolution, allowing surface features such as boulders and craters to be spotted, Chodas said. Optical telescopes around the world have been trained on Florence as well, gathering other types of data that will further flesh out researchers' understanding of the asteroid, he added. [In Photos: Potentially Dangerous Asteroids]

This flyby is like a space mission to an asteroid, "but the asteroid is coming to us," Chodas said.

This sky map by Sky & Telescope magazine shows the location of the asteroid 3122 Florence as it moves across the night sky in late August and early September 2017. The asteroid will fly within 4.4 million miles (7.1 million km) of Earth on Sept. 1. (Image credit: Sky & Telescope Magazine diagram)

Astronomers aren't the only ones who can get looks at Florence right now; the asteroid should be visible through backyard telescopes for the next few days. You can read about how to see asteroid Florence in telescopes here.

Editor's Note: If you capture a great image of asteroid Florence moving across the sky and would like to share it with Space.com and our news partners, send photos and comments to spacephotos@space.com.

Follow Mike Wall on Twitter @michaeldwall and Google+. Follow us @Spacedotcom, Facebook or Google+. Originally published on Space.com.</s>A mountain-size space rock cruised past Earth this morning (Sept. 1) in a record-breaking encounter that has long had scientists drooling.

At 8:06 a.m. EDT (1206 GMT) today, the roughly 2.7-mile-wide (4.4 kilometers) asteroid 3122 Florence came within a mere 4.4 million miles (7 million km) of Earth — just 18 times the distance from our planet to the moon.

"Nothing this big has passed this close to Earth since we've been tracking," Paul Chodas, manager of the Center for Near-Earth Object Studies at NASA's Jet Propulsion Laboratory in Pasadena, California, told Space.com. "This is a once-in-40-year-event kind of thing." [Famous Asteroid Rock Flybys and Close Calls (Infographic)]

Only 10 or so asteroids as big as Florence exist in near-Earth space, Chodas said. There was never any chance of the space rock hitting us on this encounter, and astronomers have mapped out Florence's orbit well enough to know that it poses no threat to Earth for the next few centuries at least, he stressed. (But if something as big as Florence did hit us, it would be very bad: Scientists regard any impactor at least 0.6 miles, or 1 km, across as a potential civilization-ender.)</s>A stony asteroid of the Amor group, Florence, will safely fly past Earthon September 1. However, what makes this asteroid different is its size. Classified as a near-Earth object and potentially hazardous object (PHO), it is approximately five kilometers in diameter.

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Asteroid Florence was discovered in March 1981 by American astronomer Schelte J 'Bobby' Bus at Siding Spring Observatory in New South Wales, Australia.

The asteroid will be passing by 18 times the distance between Earth and Moon, which is around 7.08 million kilometers (4.4 million miles).

ALSO READ: NASA's Juno spacecraft's 7th flyby on Sept 1: Here are 7 things to know about the mission

Though many asteroids have passed by Earth closely, Florence is found to be the biggest asteroid since NASA started keeping a track of near-Earth space asteroids.

"While many known asteroids have passed by closer to Earth than Florence will on September 1, all of those were estimated to be smaller," stated Paul Chodas, manager of NASA's Center for Near-Earth Object Studies (CNEOS) at the agency's Jet Propulsion Laboratory in Pasadena, California.

"Despite some interference from moonlight, 3122 Florence should be fairly easy to spot in even modest backyard telescopes," added Kelly Beatty, a senior editor at Sky & Telescope magazine.

The last time Florence passed by Earth was in 1890 and according to NASA, the next time it will be close to the planet again in 2500.

Asteroid Florence will appear as a 9th magnitude star without causing any danger to Earth. The space rock will be passing by Earth on Friday, at 5.30 pm IST (8 am EST).You can watch the live webcast of asteroid Florence by clicking this link.</s>Asteroid 1981 ET3, also known as Florence, will skim past Earth on September 1 at a distance of seven million kilometres.

That is about 18 times the distance between the Earth and the moon and the closest this asteroid has been since 1890.

The next time such a space rock will fly this close is in 2050, according to Nasa.

At a staggering 4.8 kilometres wide – the largest that has ever been discovered since Nasa began tracking asteroids.</s>Earth is set to be passed by the biggest asteroid ever recorded tomorrow and both astronomers and enthusiasts will be able to watch the whole thing.

Asteroid Florence will skim past Earth at around 1pm BST tomorrow (September 1) at a distance of 4.4 million miles (7.0 million kilometers).

That's roughly 18 times the distance to the moon and close enough to categorise it as a near-Earth asteroid .

NASA will be monitoring the asteroid as it passes and will use the occasion to test out various tracking technologies.

Using radar arrays here on the ground, the space agency reckons it can capture pictures of Florence with surface details as small as 10m (30 feet).

Meanwhile, you can watch it live thanks to the Virtual Telescope Project.

The live stream will start at 8.30pm BST this evening and monitor the asteroid on its path.

See it in the night sky

If you want to try and spot Florence in the night sky yourself then you're going to need a telescope, or at least a pair of binocular.

The space rock measures 2.7 miles (4.4 kilometers) across and will be very bright tonight (August 31). As well as a telescope, would-be watchers will need a good sky chart to plot its path across the sky.

"Florence shines at peak magnitude of 8.7 tonight (August 30th) and remains brighter than magnitude 10 through September 5th," wrote Bob King in astronomy site Sky and Telescope .

"That means that even with a semi-bright Moon in the sky, some of you will be able to pick it up in binoculars, and anyone with a 4-inch or larger telescope should kill it."

Is it going to hit Earth?

Although the asteroid is being labelled as "potentially hazardous", there's no chance it's going to hit us.

However, if it did, the size of it would cause mass destruction to our planet.

The asteroid that wiped out the dinosaurs is believed to have measured six miles across. Florence measures roughly half that and so would still cause cataclysmic damage.

“Florence is the largest asteroid to pass by our planet this close since the NASA program to detect and track near-Earth asteroids began,” said Paul Chodas, manager of NASA’s Center for Near-Earth Object Studies (CNEOS) at the agency's Jet Propulsion Laboratory in Pasadena, California.

The space agency is currently developing a plan to steer away any larger asteroids on a collision course with Earth through a deliberate impact. However, it requires the experts to be able to accurately locate and track incoming asteroids before it's too late.</s>An asteroid the size of a mountain just streaked by Earth on the morning of September 1 – a record-breaking phenomenon that has had scientists on the edge of their seats.

Asteroid 3122 Florence, roughly 2.7 miles wide, cruised within only 4.4 million miles from Earth, Space.com reports. This is just 18 times the distance from here to the moon.

Paul Chodas, manager of the Center for Near-Earth Object Studies at NASA’s Jet Propulsion Laboratory in Pasadena, California, said,

There have only been around 10 asteroids as big as Florence that have come close to this planet, Chodas said. There was never any danger of the giant rock hitting the Earth on this encounter, and astronomers have determined the asteroid’s path enough to know that it poses no immediate threat for the next few centuries.

If, however, an asteroid of a similar size were to hit this planet, the results would be catastrophic: scientists predict that anything causing an impact greater than 0.6 miles across would mean the end of civilization.

Florence was first discovered by astronomer Schelte “Bobby” Bus in 1981 at Australia’s Siding Spring Observatory. This massive rock orbits the sun every 2.35 years on an elliptical path. It is also a very fast spinner, scientists have observed, completing one rotation every 2.4 hours.

Chodas said, “If it were spinning any faster, it would fly apart. What often happens is, asteroids that are spinning this quickly rearrange into the shape of a top, where they have kind of a bulge at the equator.”

This is just a theory, as there is not much information on Florence – most of what is known are estimates. “There’s a lot to learn about this little world,” Chodas said. Radar images on this recent flyby have revealed more information, as NASA’s Goldstone Solar System Radar in California and the Arecibo Observatory in Puerto Rico were able to get better looks at the asteroid.

The asteroid should be visible on the night sky through a telescope for the next few days.</s>NASA has confirmed that a large asteroid known as Florence will fly past Earth at around 1pm BST on September 1, at a distance of 4.4 million miles (7.0 million kilometers).

That's roughly 18 times the distance to the moon and is close enough to categorise Florence as a near-Earth asteroid .

It's also one of the largest rocks the space agency has ever detected since it began monitoring passing asteroids. The experts believe it is around 2.7 miles (4.4 kilometers) in size.

“While many known asteroids have passed by closer to Earth than Florence will on September 1, all of those were estimated to be smaller,” said Paul Chodas, manager of NASA’s Center for Near-Earth Object Studies (CNEOS) at the agency's Jet Propulsion Laboratory in Pasadena, California.

“Florence is the largest asteroid to pass by our planet this close since the NASA program to detect and track near-Earth asteroids began.”

Because of its size, NASA thinks Florence is an excellent target to test out its various asteroid observation technologies.

Using radar arrays here on the ground, the space agency reckons it can capture pictures of Florence with surface details as small as 10m (30 feet).

"When these small, natural remnants of the formation of the solar system pass relatively close to Earth, deep space radar is a powerful technique for studying their sizes, shapes, rotation, surface features and roughness, and for more precise determination of their orbital path," explained NASA.

A smaller asteroid is also on track to pass by the Earth in October and that one will come a lot closer.

The asteroid, which is roughly the size of a house, will pass very close to Earth in October, giving scientists a chance to try out their planetary defence system.

Known as 2012 TC4, the asteroid was first spotted by the Pan-STARRS observatory in Hawaii in 2012, but its orbit meant that it could not be tracked.

Early observations indicated that it could come as close as 4,200 miles from the Earth's surface - well within the ring of geostationary satellites.

However, new observations by the European Southern Observatory's Very Large Telescope in Chile reveal that it will miss our planet by 27,000 miles - roughly one-eighth of the distance to the Moon - which is very close in astronomical terms.</s>Asteroid 3122, named after Florence Nightingale, will reach its peak brightness tonight (Thursday August 31 into Friday September 1). But the asteroid will actually be closest to Earth at 8am EDT (1pm BST) tomorrow (Friday September 1), according to Sky & Telescope magazine. The asteroid will come as close as 4.4 million miles (7 million km) to Earth but NASA has confirmed that it will not hit our planet. Paul Chodas, manager of NASA’s Center for Near-Earth Object Studies, said: “Florence is the largest asteroid to pass by our planet this close since the NASA program to detect and track near-Earth asteroids began.”

The asteroid, which is an incredible 2.7 miles (4.4 km) in size, last came this close in 1890. It will not skim so close again until after 2,500. Astroid Florence will be more difficult to see at the point when it comes closest to Earth because it will be daylight. Sky & Telescope magazine says the best time to see the asteroid with a telescope will be late this evening when it is high overhead. Senior editor Kelly Beatty said: "Despite some interference from moonlight, 3122 Florence should be fairly easy to spot in even modest backyard telescopes.”

Alternatively, you can watch a live stream of Asteroid Florence above tonight. Watch the Virtual Telescope Project live stream from 8.30pm BST (3.30pm EDT) to see the Asteroid Florence 3211 close encounter. Robotic telescope service Slooh is also showing a live stream of the Asteroid on its website at 2am BST (9pm EDT). If you miss the asteroid tonight, you have still got a chance of seeing it over coming nights.</s>The giant space rock will cruise past Earth at a distance of 4.4 million miles - roughly 18 times the distance between Earth and the moon. Asteroid 3122 Florence, which has not been this close since 1980, is the largest asteroid to have been discovered by Nasa since records began.

Where can you watch the asteroid? The asteroid should already be visible through telescopes, according to Sky & Telescope magazine. Kelly Beatty, senior editor at the magazine, said: "Despite some interference from moonlight, 3122 Florence should be fairly easy to spot in even modest backyard telescopes.” Sky & Telescope has detailed charts to help with locating the asteroid on its website.

You can also live stream Asteroid Florence online for free. The Virtual Telescope Project will begin a free webcast from 8.30pm tonight. Online observatory Slooh will also broadcast a live stream of the asteroid on its website from 2am on September 1. Slooh said: “At the moment of Florence’s approach, Slooh will train its telescopes on the asteroid to bring you its close pass live, along with commentary from our team of astronomers and asteroid experts.

“We’ll be discussing the importance of studying Near-Earth Asteroids like Florence, not only for what they can reveal about our Solar System’s past, but also due to the threat they pose to our planet. “Although 3122 Florence doesn’t pose an immediate threat to us, an impact by an asteroid its size would be catastrophic.” The Barkeep Observatory in Israel will also webcast live views on its website from 3-6pm on September 1. The best time to see the asteroid will be in the late evening, with a peak brightness expected tonight. The asteroid should be almost as bright for several days before and after the end of the month.

The asteroid, named after Florence Nightingale, was first discovered by astronomer Schelte "Bobby" Bus in 1981. Paul Chodas, manager of Nasa’s Center for Near-Earth Object Studies (CNEOS) at the agency's Jet Propulsion Laboratory, said: “While many known asteroids have passed by closer to Earth than Florence will on September 1, all of those were estimated to be smaller. “Florence is the largest asteroid to pass by our planet this close since the NASA program to detect and track near-Earth asteroids began.”</s>A massive asteroid that is nearly 3 miles wide is set to make a 'close encounter' with Earth today.

Dubbed 'Florence,' the huge space rock will pass just 4.4 million miles from our planet which is about 18 times the distance between Earth and the moon.

According to NASA, this is the closest an asteroid of this size has come since it first began tracking near-Earth objects.

Star-gazers armed with just a pair of binoculars are in with a good chance of catching a glimpse of the historic event.

For astronomers, the asteroid will give them an unprecedented opportunity to study it up close through ground-based radar observations.

HOW TO SEE IT To see the asteroid, you'll need binoculars or a telescope. Florence is most visible at 13:06 BST (08:06 ET) on 1 September as it crosses between the constellations Equuleus and Delphinus. The best places to see it pass on Friday is from Australia, New Zealand and surrounding areas as it will be night when it reaches its closest approach. North America will get a good view at local midnight about eight hours prior to its closest approach at 08:06 ET. It will also be visible on Friday night local time when it gets dark again - 16 hours after its closest approach. For people in Europe, Friday night will be the best time to catch it - around 11 hours after its closest approach. If people are unable to see it, the Virtual Telescope Project will be featuring a live stream of Florence starting on 31 August at 20:30 BST/ 15:30 ET. The best time to view will be late evening, when it's high overhead. Although Florence reaches peak brightness (magnitude 8.7) late on Thursday night (August 31st and early on September 1st), it should remain nearly this bright for several days before and afterwards. It will be gliding northward by a little less than the full Moon's diameter each hour, motion that should be obvious by watching the asteroid's starlike pinpoint through a telescope for just a few minutes.

Nearly two thirds of NEAs (near-Earth Asteroids) have a satellite and according to Nasa if Florence does have a partner chances are we will spot it in the coming days.

'Despite some interference from moonlight, 3122 Florence should be fairly easy to spot in even modest backyard telescopes,' notes Kelly Beatty, a senior editor at Sky & Telescope magazine.

The best time to view will be late evening, when it's high overhead.

Although Florence reaches peak brightness tonight it should remain nearly this bright for several days before and afterwards.

It will be gliding northward by a little less than the full moon's diameter each hour, motion that should be obvious by watching the asteroid's star-like pinpoint through a telescope for just a few minutes.

Florence appears this bright, despite being far away, both because it's among the largest near-Earth asteroids and it has a fairly bright surface that reflects more than 20 per cent of the sunlight that strikes it.

In comparison, the Moon's average reflectivity is just 12 per cent.

While it may sound alarming, NASA says asteroid Florence will safely fly past Earth at a distance of about 4.4 million miles (7 million kilometres).

It's not the closest encounter our planet has seen with an NEO, but for this distance, the experts say it is the largest.

'While many known asteroids have passed by closer to Earth than Florence will on September 1, all of those were estimated to be smaller,' said Paul Chodas, manager of NASA's Center for Near-Earth Object Studies (CNEOS) at the agency's Jet Propulsion Laboratory.

'Florence is the largest asteroid to pass by our planet this close since the NASA program to detect and track near-Earth asteroids began.'

The asteroid, named for Florence Nightingale, was first spotted in 1981, and the flyby in September will be the closest it's come to Earth since 1890.

It was first discovered in Siding Spring observatory in Australia by asteroid hunter Schelte J Bus on the night of 2 March 1981 and orbits the sun once every 859 days.

And, it won't come this close again until 2,500.

'Lots of these Earth-approachers are only visible for a matter of hours in amateur scopes before they precipitously fade from view', according to Bob King writing in Sky & Telescope.

'They're just so tiny and move so fast. Not Florence. It's neither tiny nor in a terrible hurry. Matter of fact, it's a beast'.

'Some of you will be able to pick it up in binoculars, and anyone with a 4-inch or larger telescope should kill it.'

The asteroid is large enough to end life as we know it if it hits, but NASA says this won't happen this week.

A 2016 study found a 0.6-mile-wide (1km) asteroid could trigger a mini ice age if it collided with Earth.

An impact of this size would have a 'very severe global impact' for several years and would cause the world to become a much darker, colder and drier place, experts say.

At 2.7 miles wide (4.3km) an impact with Florence could be devastating to life as we know it.

However, it would take an asteroid around 6 miles wide (9.7km) or more to cause mass extinction, according to experts from the National Center for Atmospheric Research.

Although a collision will not be happening this year, a very small change in an asteroid's motion - only be a few millimetres a second - can cause the asteroid to change trajectory.

This means that Florence could potentially pose a risk to life on Earth in years to come should its orbit change marginally.

It culminates at 13:06 BST (08:06 ET) on 1st September as it crosses between the constellations Equuleus and Delphinus.

The best places to see it pass on Friday is from Australia, New Zealand and surrounding areas as it will be night when it reaches its closest approach.

North America will get a good view at local midnight about eight hours prior to its closest approach at 08:06 ET with the next good viewing moment 16 hours after its closest approach.

For people in Europe, Friday night will be the best time to catch it - around 11 hours after its closest approach.

If people are unable to see it, the Virtual Telescope Project will be featuring a live stream of Florence starting on 31 August at 20:30 BST/ 15:30 ET.

It will take around an hour to travel a distance 2/3 the diameter of the Full Moon.

During this time, it will pass through the constellations Piscis Austrinus, Capricornus, Aquarius and Delphinus.

NASA scientists will use ground-based radar to observe its features up close, using radar imaging NASA's Goldstone Solar System Radar in California and at the National Science Foundation's Arecibo Observatory in Puerto Rico.

With these instruments, they will be able to see it's true size, and even observe surface details as small as about 30 feet (10 meters).

IMPACT WILL HAPPEN 'SOONER OR LATER' EXPERT WARNS Researchers have discovered most of the asteroids that are about a kilometers in size, but are now on the hunt for those that are about 140m - as they could cause catastrophic damage. Although nobody knows when the next big impact will occur, scientists have found themselves under pressure to predict - and intercept - its arrival. 'Sooner or later we will get... a minor or major impact,' said Rolf Densing, who heads the European Space Operations Centre (ESOC) in Darmstadt, ahead of International Asteroid Day on Friday. It may not happen in our lifetime, he said, but 'the risk that Earth will get hit in a devastating event one day is very high.' For now, there is little we can do. And yet, the first-ever mission to crash a probe into a small space rock to alter its trajectory suffered a major setback when European ministers declined in December to fund part of the project. 'We are not ready to defend ourselves' against an Earth-bound object, said Densing. 'We have no active planetary defense measures.'

Earlier this month, the space agency revealed an asteroid the size of a house set to narrowly skim the Earth in October, after it was spotted by scientists for the first time in five years.

The asteroid, dubbed 2012 TC4, first flitted past our planet in October 2012 at about double the distance of its next expected pass, before disappearing.

Now the European Space Agency (ESA) has tracked down the giant hunk of rock, which is about 15 to 30 metres (49 to 98 feet) long and roughly the size of a house.

TC4's next approach, predicted for October 12, will bring the massive object 'damn close', according to experts, when it flies inside the moon's orbit – just far out enough to miss our geostationary satellites.
Asteroid 3122 Florence, which is roughly 2.7 miles (4.4 kilometers) wide, comes within 4.4 million miles (7 million km) of Earth — approximately 18 times the distance from our planet to the Moon.