s a Star?" page and describe how stars 10 times more massive and 1/10th the Sun’s mass will be different than the Sun in terms of brightness and lifetime.
1. The Trifid Nebula, otherwise known as M20, is a place where new stars are forming. It has been called a “dark night revelation, even in modest apertures.” An 8- to 10-inch telescope is needed to see the triple-lobed structure of the nebula. Ordinary binoculars reveal the Trifid as a hazy patch located in the constellation Sagittarius. This nebula is set against the richest part of the Milky Way, the edgewise projection of our own Galaxy around the sky. It is one of many wonders in this region of the heavens. What are the dark lanes in M20? Why are other parts of the nebula bright? There have been reports of large-scale changes occurring in this nebula in the last century and a half. The reports are based on old drawings, which show M20 looking slightly different from how it appears today. Do you think it possible for a cloud in space to undergo a change in appearance on a time scale of years, decades, or centuries?
2. Summer is a good time to search with binoculars for open-star clusters. Open clusters are generally found in the plane of the Galaxy. If you can see the hazy band of the Milky Way arcing across your night sky—in other words, if you are far from city lights and looking at an appropriate time of night and year—you can simply sweep with your binoculars along the Milky Way. Numerous “clumps” of stars will pop into view. Many will turn out to be open-star clusters.
3. Globular star clusters are harder to find. They are intrinsically larger, but they are also much farther away and therefore appear smaller in the sky. The most famous globular cluster visible from the Northern Hemisphere is M13 in the constellation Hercules, visible on spring and summer evenings. This cluster contains half a million or so of the Galaxy’s most ancient stars. It may be glimpsed in binoculars as a little ball of light, located about one-third of the way from the star Eta to the star Zeta in the Keystone asterism of the constellation Hercules. Telescopes reveal this cluster as a magnificent, symmetrical grouping of stars.
|SKYCHART III PROJECTS||The SkyChart III Student Version planetarium program on which these exercises are based is included as a separately executable program on the CD in the back of this text.|
1. Appendix 3 contains a list of the 20 brightest stars. Make your own table of these stars with columns for information on the range of dates each is visible in your area at a time convenient for observation, and another column with information on how to locate each one. Make note of those stars that are not available to you because they are in the Southern Hemisphere. Use SkyChart III and the chart you have made to locate the bright stars available at this time. Along with being able to recognize the constellations, it is rewarding to know the names of the bright stars. A small effort is usually sufficient to develop a satisfying familiarity.
In addition to the Practice Problems and Destinations modules, the Companion Website at http://www.prenhall.com/chaisson
provides for each chapter an additional true-false, multiple choice,
and labeling quiz, as well as additional annotated images, animations,
and links to related Websites.