Sunday, November 11, 2007

STAR IDENTIFICATION ( PART 1)

In the north polar region everyone is familiar with the Big Dipper, the popular name for the constellation Ursa Major (the big bear). This is made up of seven stars in the shape of a dipper, with the open part toward the north celestial pole. For observers in the United States, most of the dipper is circumpolar and is visible the year around. I like to use Dubhe, Alioth, and Alkaid when taking sights. Dubhe and Merak, form part of the bowl of the dipper, are called the pointers, the line connecting them is extended northward, it passes very near Polaris, less than one degree from the north celestial pole. If the line is extended across the pole, it leads very near to Caph in Cassiopeia. These stars point sky of mid-April. By the middle of July they are to the left of Pol:;c-.s In mid-October they are directly below the pole, and three moru:i:li! later, in the middle of January, they are to the right. For other 5La:r'lt identified by means of the Big DiPper, see Article 2010.

Ursa Minor Polaris is part of the Little DiPper, as the constellation Ursa Minor little bear) is popularly known; this star is not conspicuous until
sky has become quite dark. Only Polaris at one end and Kochab at other, both second-magnitude stars, are used by the navigator. little dipper is roughly parallel to the big dipper, but upside down respect to it. In the autumn the Big DiPper is under the Little DiPper and there is a folk saying that liquid spilling out of the little one will caught by the big one. The handles of the two dippers curve in oppo­site directions, relative to their bowls.
Cassiopeia Cassiopeia (the queen), across the pole from the handle of the Big Dipper, and approximately the same distance from Polaris, you will find Cassiopeia's Chair. The principal stars of this constellation form a well-defined W or M, depending on their position with respect to the pole. Schedar, the second star from the right when the figure appears as a W, is a second-magnitude star sometimes used by navigators. Second-magnitude Caph, the right-hand star when the figure appears as a W, is interesting because it lies close to the hour circle of the vernal equinox.
Draco is about halfway from Cassiopeia to the Big Dipper in a westerly direction, but its navigational star Eltanin probably is more easy to identify by following the western arm of the Northern Cross.

Bootes, Virgo the spring sky in the spring, the Big Dipper is above the pole, high in the sky, and serves to point out several excellent navigational stars. Starting at the bowl, follow the curvature of the handle. If this curved arc is continued, it leads first to Arcturus, the only navigational star in Bootes (the herdsman) and then to Spica in Virgo (the virgin), both first-magnitude stars used by the navi­gator. A line northward through the pointers of the Big Dipper leads to Polaris. If this line is followed in the opposite direction, it leads in the general direction of Regulus, the end of the handle of the sickle Leo in the constellation Leo (the lion). This used navigational star is of the first magnitude and the brightest star in its part of the sky. A line connecting Regulus and Arcturus passes close to second-magni­tude Denebola (tail of the lion), sometimes used by navigators.
Corvus Corvus (the crow) is not difficult to find and is a third-magnitude navigational star Gienah. Due south of Corvus is the Southern Cross. Alphard is a second magnitude star it is identified by being close to the pointer of the big dipper. Scorpio (summer triangle) is great for taking sights,these stars are Vega, Deneb, and Altair. I always try to take a sight on at least one of these stars.