September: Lyres and Swans

September 2011

Lyres and Swans

By Calvin L. Chrisman

The beautiful trio of stars known as the Summer Triangle is actually at its highest near the end of summer. To find it, first go out shortly after dusk and look toward the zenith, the spot in the sky that is directly over your head. You will see a bright star known as Vega. Vega is in Lyra, the lyre. Below Vega is the parallelogram of four stars that makes up the lyre. This is one of the smallest constellations in the sky. Once you have spotted Vega, look for Altair to the south and Deneb to the east. Vega and Altair are 25 and 16 light years from us while Deneb is approximately 1500 light years away. Because of its distance, Deneb appears to be no brighter than the others; it is actually one of the most powerful stars in the sky. It is 25 times more massive and 60,000 times more luminous than our Sun.

Deneb is in Cygnus the Swan. In fact, Deneb means “tail” in Arabic. (The root “Deneb” is also found in the name of the star Denebola – the tail of the constellation Leo, the lion).  As you look at Deneb, you will see that it is part of a pattern that looks like a cross. Some call it the Northern Cross (if the southern hemisphere has the Southern Cross, why shouldn’t we have our own?). Representing the head of the swan or the foot of the cross is Albireo.  If you have a telescope, take a close look at Albireo. It is a double star with striking color contrast between the pair. One is golden yellow while the other is blue; an interesting sight. If you spend some time looking at Cygnus near the end of the month when the moon is dark, you will see that it is situated in the middle of the Milky Way and that the stars appear to divide into two streams in Cygnus. This is due to a dust cloud darkening that area of sky.

There are several stories of Cygnus. One says that it is Orpheus who sang and played his lyre so well that wild animals and even trees would come to hear. As a result, the gods transported him to the skies as a swan so that he could be near his lyre. Another story is that Cygnus is Zeus disguised as a swan as he was when he seduced Leda.

Your kids may think summer is over since they have been in school for a while now. Astronomically speaking, it ends on September 23 at 5:05 a.m. EDT. The sun will set due west on that day as it crosses the Earth’s equator on its way south for the winter. By the end of the month, brilliant Jupiter will be rising at dusk and Mars will be visible in the pre-dawn sky.

Clear Skies!

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