Circumpolar Constellations Help (page 2)
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.
The so-called big dipper is formally known as Ursa Major , which means “big bear.” It is one of the most familiar constellations to observers in the northern hemisphere. In the evening, it is overhead in the spring, near the northern horizon in autumn, high in the northeastern sky in winter, and high in the northwestern sky in summer. It, like its daughter, Ursa Minor, is shaped something like a scoop (Fig. 2-2). The two stars at the front of the scoop are Dubhe and Merak , and are called the pointer stars because they are roughly aligned with Polaris. If you can find the big dipper, look upward from the scoop five or six times the distance between Dubhe and Merak, and you will find Polaris. To double-check, be sure that the star you have found is at the end of the handle of the little dipper.
One of the north circumpolar constellations is known for its characteristic M or W shape (depending on the time of night and the time of year it is viewed). This is Cassiopeia , which means “queen.” Ancient people saw this constellation’s shape as resembling a throne (Fig. 2-3), and this is where the idea of royalty came in. In the evening, Cassiopeia is low in the north-northwestern sky in the spring, moderately low in the north-northeastern sky in the summer, near the zenith in the fall, and high in the northwestern sky in the winter.
As the queen sits on her throne, she faces her spouse, the king, the constellation whose formal name is Cepheus . This constellation is large in size but is comprised of relatively dim stars. For this reason, Cepheus is usually obscured by bright city lights or the sky glow of a full moon, especially when it is near the horizon. It has the general shape of a house with a steeply pitched roof (Fig. 2-4). In the evening, Cepheus is near the northern horizon in the spring, high in the north-northeast sky in the summer, nearly overhead in the fall, and high in the northwestern sky in the fall.
One of the largest circumpolar constellations, obscure to casual observers on account of its long, winding shape, is Draco , the dragon. With the exception of Eltanin , a star at the front of the dragon’s “head,” this constellation is made up of comparatively dim stars (Fig. 2-5). Draco’s “tail” wraps around the little dipper. The big dipper is in a position to scoop up the dragon tail first. In the evening, Draco is high in the northeastern sky in springtime, nearly overhead in the summer, high in the north-northwest sky in the fall, and near the northern horizon in the winter.
Perseus is another circumpolar constellation with an elongated, rather complicated shape (Fig. 2-6). A mythological hero, Perseus holds the decapitated head of Medusa, a mythological female monster with hair made of snakes and a countenance so ugly that anyone who looked on it was turned into stone. Perseus is low in the northwestern sky in springtime, half above and half below the northern horizon in the summer, high in the northeastern sky in the fall, and nearly overhead in the winter.
Practice problems of this concept can be found at: Stars and Constellations Practice Problems
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