Circumpolar Constellations Help
Star Brightness and Polaris
In this chapter, stars are illustrated at three relative levels of brightness. Dim stars are small black dots. Stars of medium brilliance are larger black dots. Bright stars are circles with black dots at their centers. But the terms dim, medium, and bright are not intended to be exact or absolute. In New York City, some of the dim stars shown in these drawings are invisible, even under good viewing conditions, because of scattered artificial light. After your eyes have had an hour to adjust to the darkness on a moonless, clear night in the mountains of Wyoming, some of the dim stars in these illustrations will look fairly bright. The gray lines connecting the stars (reminiscent of dot-to-dot children’s drawings) are intended to emphasize the general shapes of the constellations. The lines do not, of course, appear in the real sky, although they are often shown in planetarium presentations and are commonly included in sky maps.
One special, moderately bright star stays fixed in the sky all the time, day and night, season after season, and year after year. This star, called Polaris , or the pole star , is a white star of medium brightness. It can be found in the northern sky at an elevation equal to your latitude. If you live in Minneapolis, for example, Polaris is 45 degrees above the northern horizon. If you live on the Big Island of Hawaii, it is about 20 degrees above the horizon. If you live in Alaska, it’s about 60 to 65 degrees above the horizon. At the equator, it’s on the northern horizon. People in the southern hemisphere never see it.
Polaris makes an excellent reference for the northern circumpolar constellations and in fact for all the objects in the sky as seen from any location in Earth’s northern hemisphere. No matter where you might be, if you are north of the equator, Polaris always defines the points of the compass. Navigators and explorers have known this for millennia. You can use the pole star as a natural guide on any clear night.
Polaris rests at the end of the “handle” of the so-called little dipper. The formal name for this constellation is Ursa Minor , which means “little bear.” One might spend quite a while staring at this constellation before getting the idea that it looks like a bear, but that is the animal for which it is named, and whoever gave it that name must have had a reason. Most constellations are named for animals or mythological figures that don’t look anything like them, so you might as well get used to this. The general shape of Ursa Minor is shown in Fig. 2-1. Its orientation varies depending on the time of night and the time of year.
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