Southern Circumpolar Constellations Help
Introduction to Southern Circumpolar Constellations
Star Brightness and Polaris
In this chapter, as in Chapter 2, 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 downtown Sydney, 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 outback, some of the dim stars in these illustrations will be easy to see. The gray lines connecting the stars are included in the diagrams only to emphasize the general shapes of the constellations.
There Is No Southern Polaris
We need a time of reference for our circumpolar observations, and mid-April is as good a time as any. Imagine that you are in the countryside near Sydney or Cape Town or Buenos Aires and that you go outdoors to stargaze at around 10:00 Assume that the sky is clear, there is no haze, and the Moon is below the horizon so that its light does not interfere with stargazing. You know that the south celestial pole is 35 degrees above the southern horizon. You search for a significant star, or at least a constellation, to mark the spot using the “fist rule.” (Hold your right arm out straight and make a tight fist. Point the knuckles toward your right. The top of your fist is about 10 angular degrees from the bottom.) You find the southern horizon using a compass or your knowledge of the area and proceed three and a half fists up into the sky. There is nothing significant. The south polar region is devoid of bright or even moderately bright stars. This caused some trouble for mariners who ventured south of the equator. They needed a convenient way to locate the south celestial pole.
Crux And Musca
As you stand facing toward the south, you will see, high in the sky, a group of four stars forming a kitelike shape. This is Crux , more commonly called the southern cross . Just below it, somewhat dimmer, is a star group shaped somewhat like a ladle. This is Musca or Musca Australis , the southern fly . Look at these two constellations carefully, and make educated guesses as to their centers (Fig. 3-5). The center of Crux is easy to decide on, but the center of Musca is a little tougher. Pick a point on the handle of the ladle, just above the scoop. These two constellation-center points are separated by about 10 degrees of arc, a fact that you can verify by the fist rule. Now go two fists down toward the southern horizon from the center point of Musca. This will give you a point close to the south celestial pole.
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