This is Dudley Observatory’s Skywatch Line for Wednesday, October 13, and Thursday, October 14, written by Alan French.
The Sun sets at 6:16 P.M. on Wednesday and rises at 7:08 A.M. Thursday. Sunset Thursday is at 6:14 and the Sun will rise at 7:09 on Friday.
The Moon reached first quarter late Tuesday evening so a waxing gibbous Moon will grace our evening sky. The Moon will reach full on Wednesday, October 20.
At 7:45 P.M. Wednesday night the Moon will be low in the south, 22 degrees above the horizon, and 59 percent illuminated. It will lie among the stars of the constellation Capricornus and Saturn will be just under 7 degrees to the Moon’s upper left.
On Thursday night the Moon will be due south at 8:40 P.M., still in Capricornus, 24 degrees above the horizon, and 70 percent illuminated. It will lie between the gas giants, Jupiter and Saturn, with bright Jupiter 8 degrees to the Moon’s upper left and fainter Saturn 10 degrees away to the upper right.
The Moon sets at 12:19 A.M. Thursday and 1:30 A.M. Friday.
Look low toward the northeast around 9:30 P.M. A bright star, about 20 degrees above the horizon, should catch your eye. This is Capella, the Goat Star, the brightest star in Auriga, the Charioteer. Before the internet and widely available planetarium software, this writer often got calls during the fall asking about the bright star in the northeast in the early evening. When low in the sky it certainly draws people’s attention.
Like most bright stars, Capella is bright because it is a close neighbor, lying only 42 light-years from our Sun. It is the sixth brightest star in the night sky, the third brightest in the northern celestial hemisphere, and the closest to the north celestial pole, which lies near Polaris.
Many of the stars in the night sky, although appearing as single stars to the eye, are actually multiple star systems. Many can be resolved – seen as multiple stars – through a telescope, but some simply appear too close together to be detected by eye, even with a aid of a telescope. But when their light is spread out into its spectrum by prisms, their multiple nature is revealed.
In 1899 William Wallace Campbell of Lick Observatory announced that spectroscopic studies had shown Capella was a double star. The shifting spectrum of the companion revealed it was alternately moving toward and away from Earth, showing that the companion was orbiting Capella.
We now know that Capella is actually, at least, a quadruple star system.