Thursday, January 06, 2005

Winter Stars Are Brighter

Winter Stars Are Brighter
by Dave Adalian

Nights in winter seem starrier partially due to drier air overhead, but mostly because there are just more bright stars in the winter sky.

Winter begins with the Summer Triangle of Vega, Deneb and Altair lingering in the west after sundown. These jewels set quickly, and on the opposite side of the sky the Winter Hexagon’s easternmost members emerge.

By 7 o’clock, Sirius is high enough for viewing east of Orion’s belt. The Dog Star shines from 8.6 light years away in Canis Major, but because it is 20 times brighter than our sun remains the brightest star that can be seen from Earth at magnitude -1.4.

Sitting at due east and rising just before Sirius is a magnitude-0.0 star 11.4 light years distant. Because it rises just ahead of Sirius it’s known as Procyon, which means before the dog. A double star, its companion is a tiny, invisible white dwarf.

To the northwest, the third corner of the Hexagon is occupied by Castor and Pollux, the twins of Gemini. Between the twins and Procyon lies bright yellow Saturn, which will be much in the news later this month when the Huygens probe lands on its moon Titan.

Pollux, a magnitude-1.1 star 33.7 light years distant, glows orange. Farther, dimmer Castor--magnitude 1.6 at 51.5 light years--appears white to the eye. Through a telescope Castor becomes three stars, and though not visible each of these is a double for a total of six suns looking like one to the naked eye.

Above and right of the Twins is Capella, the fourth corner of the Hexagon and the sky’s sixth brightest star at magnitude 0.1. It shines from 41 light years away in Auriga the Charioteer.

Lower and farther right is Aldebaran, the red eye of Taurus the Bull, occupying the fifth spot at 60 light years away and magnitude 0.9.

Completing the Hexagon is Rigel, brightest of stars in Orion and just right of his belt. Even though it is some 1,400 light years away, Rigel still shines at magnitude 0.5, making it seventh brightest as seen from Earth.

While Rigel officially ends the lap around the Winter Hexagon, many find it natural to make a sharp left to finish up at magnitude 0.5 Betelgeuse, which also sits some 1,400 light years distant. This red giant is nearing the end of its life, making it a prime candidate to go supernova.


This column originally appeared in the Visalia (Calif.) Times-Delta on Jan. 6, 2005.