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May 20, 2024

Backyard Astronomy: The Birds of Summer (2003-07-14)

By Cheryl Haimann

The Summer Triangle is moving higher in the sky, with topmost star Vega (and its constellation, Lyra) almost straight overhead at midnight. This makes nightfall the perfect time to look at the other constellations in the triangle.
Summer Triangle
On the base of the triangle, the left star is Deneb. The name is similar to Denebola, the tail star in Leo, and in fact, Deneb does mean "tail." In this case, it is the tail of Cygnus (SIG-nus), the Swan. It looks like a bird in flight, its long neck extended to the right. Cygnus is also sometimes called the Northern Cross. Right now the cross is lying on its side, but as summer turns to fall and the constellation moves to the west, it will indeed resemble an upright cross.

While many civilizations have identified this group of stars as a bird, the origins of the swan legend are a bit murky. Possibly it is Orpheus, a Thracian hero who sang and played the lyre so beautifully that he was placed near a lyre in the sky. Or it may be Cyncus, who gathered up the bones of his pal Phaethon after Phaethon's joyride in his dad's Sun Chariot ended badly. It may even be Zeus in swan drag, out to find himself a Spartan girlfriend.

In moderately dark skies, you will be able to see that the Milky Way runs the length of the flying swan. In very dark skies, you may even see that the Milky Way splits into two streams just below the swan. This split is actually a dark nebula. Unlike other nebulae that glow or reflect light, dark nebulae can only be identified when they block out something in an otherwise rich field of stars, such as the Milky Way. It is thought that dark nebulae may be areas in the earliest stages of star formation.

Alberio (al-BEER-ee-oh), the head of the Swan, is an easy and fun target in a telescope. It is actually two stars - one golden yellow, and the other blue.

The third star of the triangle, Altair, is the tail of Aquila (uh-KWILL-ah), the Eagle. The Eagle belonged to Zeus and carried out nefarious tasks for him, such as nightly eating the (self- regenerating) liver of Prometheus. Aquila is also positioned along the Milky Way.

Midway between Altair and Alberio is tiny Sagitta (sah-JIT-ah). Most civilizations have recognized this grouping as an arrow. It may represent the arrow Hercules used to kill Aquila.

July Moon Watch: The Moon was full on Sunday, and is now waning, or becoming smaller. The left half is spherical, and the right half will decrease each day of the waning gibbous phase. The Moon will also rise later each night, and be visible in the early morning.

On Wednesday, July 16, the Moon will rise about 11:00 PM local daylight saving time. Bright Mars will be to its left. Early Thursday morning, they will be even closer, and in southern Florida or points south, it will be possible to see the Moon occult (cover) Mars.

This week in Moon history: July 20 is 34th anniversary of the Apollo 11 Moon landing.
Article © Cheryl Haimann. All rights reserved.
Published on 2003-07-14
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