Tonight’s chart has you looking eastward at the famous Summer Triangle. Today, notice the star Deneb, the northernmost star in the Summer Triangle. Its constellation is Cygnus the Swan. In a dark country sky, you can see that Cygnus is flying along the starlit trail of the summer Milky Way.
The photo below is from Annie Lewis in Spain. She solved the problem of picking out the Summer Triangle from among many stars in the night sky by looking for the Triangle in the east soon after sunset. These three stars are, after all, among the brightest in the sky.
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EarthSky Facebook friend Annie Lewis in Madrid, Spain, captured this photo of the Summer Triangle shortly after nightfall on a summer night. In fact, she said, the only stars visible to the unaided eye when she took the photo were the three in the Triangle. But her camera knew better. Thanks, Annie.
If it’s darker out, you might recognize the Summer Triangle by noticing that there is a cross within the Triangle. The constellation Cygnus is that cross. In fact, the constellation Cygnus is sometimes called the Northern Cross.
Okay, I’ve given you a lot of names here: Summer Triangle, Cygnus, Northern Cross.
Just remember, the constellation Cygnus the Swan contains the Northern Cross. The Cross is – more or less – just another way to see the Swan. The Northern Cross is what’s called an asterism, or recognizable pattern within a constellation. In this case, the pattern is the whole constellation, pretty much. At least, I never see them any differently.
Except for one thing. Deneb is at the top of the Cross, but at the tail of the Swan (the star name “deneb” always means “tail”). The little star Albireo is at the head of the Swan, but at the base of the Cross. Whew!
Our Summer Triangle series also includes:
Part 1: Vega and its constellation Lyra
Part 3: Altair and its constellation Aquila
Bottom line: The Summer Triangle consists of 3 bright stars in 3 different constellations. Deneb is the tail of Cygnus the Swan.
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Source:
https://earthsky.org/tonight/summer-triangle-deneb-and-its-constellation-cygnus-2