Night Two (Pt. 2): More Summer Triangle

Observed on September 12, 2011, approximately 8:30 pm CDT

This is a continuation of Patio Stargazing.

It has been very cloudy, cool, and rainy in Chicago over the last week. In other words, it’s been impossible to see the night sky. It feels like we skipped Early Fall and moved right into Late Fall. Nonetheless, when the skies clear, it will still be easy to spot the three bright stars of the Summer Triangle.

Summer Triangle with stars in Cygnus and Aquila

Again, Vega is the brightest, and the highest overhead. Deneb is the least bright of the three, and it is to the left and slightly below Vega. Now that it is late September (almost early October), my sketch is a little off. Deneb is now closest to the point directly overhead in the early evening with Vega to the right and slightly lower (toward the western horizon).

Whereas Vega is very bright because it is relatively close to us, Deneb is just bright, incredibly bright. It is over 3200 light years away (or over 100x farther than Vega). Imagine how bright a beacon Deneb must be to be seen so easily in our night sky. Finally, Altair is well below Vega and Deneb, and almost as bright as Vega. In fact, Altair is even closer to us than Vega is (just 17 light years away).

During my night of patio stargazing, I spotted four more stars. The sky was not dark enough to see any others in the vicinity of the Summer Triangle. Three of these stars form a line near Deneb and, like Deneb, are part of the constellation of Cygnus (the swan). From top to bottom, they are Delta Cygni (or Rukh), Gamma Cygni (or Sadr), and Epsilon Cygni (or Gienah). Rukh is notable for being a triple star. Sadr is the brightest of the three. The traditional names of two of these stars are appropriate for a constellation named for a swan: Sadr comes from the Arabic for chest and Gienah comes from the Arabic for wing.

Cygnus (the swan) is also known as the Northern Cross, but you wouldn’t know it from the pattern of stars I saw in the city. The three stars (Rukh, Sadr, and Gienah) form the short leg of the cross. There is a fifth star in Cygnus (called Albireo) that, had the sky been dark enough to see it, forms the long leg of the cross with Deneb and Sadr. In my sketch above, Albireo would be found somewhere below the letter s in the word “swan.”

Another bird constellation, Aquila (the eagle), is home to the fourth additional star I saw that night. This star, located very close and to the right of bright Altair, is Gamma Aquilae, with the traditional name Tarazed. The name probably comes from the Persian for “the beam of the scale,” thus proving that where one group of people saw an eagle, another group of people saw a balancing scale—and I saw just two stars.

Look for the three bright stars of the Summer Triangle later this fall and reminisce about the warmer days and nights that have passed us by. As the days and weeks pass, in the early evening sky the stars of the Summer Triangle will approach the western horizon, eventually disappearing into the dusk twilight by winter. Hope for clear skies soon!

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