Even though we're well into the holiday season, there's still some summer in the cold evening skies.
In July and August the summer constellations were soaring nearly overhead, but now the last of them are still hanging in there in the western sky. Meanwhile, in the eastern heaven the winter constellations like Orion are on the rise. In between we have autumn constellations like Pegasus and Andromeda. Just like the professional and amateur sports season, there is overlap.
You can blame Earth's orbit around the sun for the demise of the summer constellations. As we circle the sun, our view from the night side of our planet out into space is slowly but constantly changing. That's why we have different arrays of constellations in our evening heavens from season to season.
If you observe the evening sky, say around 7 tonight (or the next clear night), and then look about a month from now at 7 p.m., you'll see that the constellations in the eastern sky have become higher in the sky and the stars in the western sky are lower. Eventually we "lose" the western constellations as they're already below the western horizon by the time night sets in.
Among my favorite summer constellations headed for the celestial exits are Aquila the Eagle, Cygnus the Swan, and Lyra the Harp. At the start of each evening, these constellations are perched a little above the west-northwestern sky. Just look in the western half of the sky for a triangle of the three brightest stars you can see. This is known as the "Summer Triangle." All three of these stars are the brightest in their respective constellations.
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See the swan
The highest one is Deneb, the brightest star in the constellation Cygnus the Swan. Deneb is a humongous star that may be over 90 million miles in diameter. Our own sun isn't even a million miles in girth.
The best way to see Cygnus as a Swan is to first see the asterism within it called the Northern Cross. It's so easy to see it this time of year as the cross is nearly upright in the western sky. Deneb marks the top of the cross and below you can easily see three bright stars in a horizontal row that make up the crosspiece . A little way below the cross piece is a dimmer star but seeable with the naked eye. That's Albireo at the base of the Northern Cross. Again it's so easy to see.
You may have heard of an actual constellation best seen in the southern hemisphere called the Southern Cross. I've actually seen it and while it's a prominent constellation I really think the Northern Cross is a much more perfect cross and certainly much larger in the sky than the Southern Cross.
To make the Northern Cross into a swan is easy. Make Deneb the tail of the swan and Albireo the head. On both ends of the crosspiece stars you'll see two dimmer stars to the upper right of the right hand star of the crosspiece and a single dimmer star to the upper left of the left hand star of the crosspiece. Join them all together from end to end and that makes up the wingspan of Cygnus that's winging the swan to the western horizon.
Headless eagle
The star on the lower left corner of the Summer Triangle is Altair, a star about 16 light years from our backyard, That bright shiner marks the heart of Aquila, a headless eagle. Altair is part of a horizontal sideways diamond. Most of the rest of this constellation is shaped like a giant sideways diamond that outlines the wingspan of Aquila. Below the diamond, a few fairly dim stars mark the eagle's tail. They may be a little hard to see because they're so low in the sky.
Aquila in Greek mythology was Zeus's faithful pet eagle and part-time enforcer. The aggressive eagle would carry on many a mission for the king of the Greek gods. Aquila would fly down from Mount Olympus to punish law-breakers or anyone one that angered Zeus. He had a razor-tipped beak and talons. It certainly wasn't what you would call humane justice!
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Once a vulture
The brightest star of the Summer Triangle is Vega, on the lower right corner. The light we see from this star tonight originally left that star when George Hubert Walker Bush was president in 1990. Vega is also the brightest star in the tiny constellation Lyra the Lyre, which is an old fashioned harp. Look for four faint stars that you can barely see with the naked eye to the left of Vega that form a small parallelogram and that's supposed to outline a diminutive harp in the sky.
Actually, up until the time of the American Revolution, all three of the summer triangle constellations were seen as birds. Lyra the Harp was actually pictured as an Eagle clasping a small harp in its beak. In fact, over 2,000 years ago ancient India saw what we see as Lyra the Harp as a vulture. Many Arabic cultures about the same time saw the constellation as a desert eagle.
So while you're gazing in the heavens these cold pre-winter evenings, say a final farewell to summer, or at least the birds of summer, all three of the winged fowl. They won't appear in the evening sky again until next June, when they'll be on the rise in the east.
Bye, bye, birdies!
Celestial huggings this week:The waning crescent moon and the very bright planet Venus will have a spectacular conjunction Monday morning in the pre-twilight low southeast sky. Venus is the brightest star-like object in the sky in the early morning and the crescent moon will be just to the upper right of it. Don't miss it. If it's cloudy and you don't see it, try again on Tuesday morning. It won't be as great, but Venus and the moon will still be pretty close, with moon hanging out to the lower left of Venus. On both mornings it's well worth it to wake up early and take in the show!
