There are ten first magnitude objects on this month's star chart, drawn for the beginning of April about 8:15 p.m. standard time, or 9:15 p.m. daylight time. In order of brightness, from brightest to faintest, they are Sirius in Canis Major the Large Dog, Arcturus in Bootes the Herdsman, Capella in Auriga the Charioteer, Rigel in Orion the Hunter, Procyon in Canis Minor the Little Dog, Betelgeuse in Orion the Hunter, Aldebaran in Taurus the Bull, Spica in Virgo the Maiden, Pollux in Gemini the Twins, and Regulus in Leo the Lion. If you wait another 1 ½ hours, these ten will be joined by an eleventh first magnitude star, Vega in Lyra the Harp, which goes into our list between Arcturus and Capella.

         Sirius, the Dog Star, is the brightest star visible from Earth, exclusive of our Sun, of course. It is a relatively near neighbor at a distance of only 8.7 light years. A surface temperature nearly twice as high as Sun's and a diameter almost twice Sun's make it 23 times as luminous. Arcturus is the fourth brightest star visible from Earth. Arcturus is 37 light years distant and is classified a giant -- its diameter is about 25 times Sun's and it is 115 times as luminous as Sun, though its surface temperature is more than a thousand degrees cooler than Sun's.

        Vega in Lyra the Harp shines at +0.03 magnitude and is the fifth brightest star. Its distance is about 27 light years. With a surface temperature nearly twice that of Sun and a diameter about 3 times Sun's, it is 58 times as luminous as Sun. Capella, sixth brightest star, is really a spectroscopic binary, two stars with a combined luminosity 160 times Sun's. This pair is 45 light years from us. The two stars are too close to be resolved in a telescope. That there are two stars is deduced from the periodic Doppler shifts of the spectral lines in their combined spectra, the characteristic from which they get the name "spectroscopic" binary.

         Rigel, the seventh brightest, is Orion the Hunter's left knee if we picture him facing us. Rigel is one of the most intrinsically luminous stars known. It is approximately 1400 light years away with a luminosity 57,000 times that of Sun. It is a blue giant with a surface temperature higher than Sirius's and a diameter 50 times Sun's. If Rigel were at the distance of Sirius, we would receive nearly as much light from Rigel as from the first quarter moon. Procyon is one of only two or three stars we can see in Canis Minor. It is the eighth brightest star and is 11.3 light years away. It has a surface temperature a little higher than Sun's and a diameter a little more than twice Sun's, making it about 6 times as luminous as Sun.

        Betelgeuse is Orion's right shoulder. It is about 520 light years away and is only half as hot as Sun. It is a variable star, varying in brightness because its diameter varies between about 550 and 920 times Sun's diameter. It is truly a supergiant, for if it were at Sun's location, its surface would be beyond the orbit of Mars. Aldebaran is the red giant that forms the eye of Taurus the Bull, and is the thirteenth brightest. It is about 68 light years away. Spica is the fifteenth brightest star at a brightness of 1.00 magnitude. Its surface is hotter than Rigel's, but its diameter is only about 8 times Sun's diameter, so its luminosity is only about 2300 times our Sun's.

        Pollux is the eastern-most of the Twins and is the seventeenth brightest star. It is a yellow giant, cooler than Sun, but about 5 times the diameter of our star. Finally, Regulus, the Heart of Leo the Lion, is the hottest of the bright stars visible in the April sky, about a thousand degrees hotter than Rigel, but not a giant. Rather, its diameter is only about 5 times Sun's, making it 160 times as luminous as Sun.