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How to see the Summer Triangle in September


Tonight for September 12, 2014

The Summer Triangle consists of three bright stars in three separate constellations. The stars are Vega in the constellation Lyra, Deneb in the constellation Cygnus, and Altair in the constellation Aquila. These stars should be clearly visible, despite the glare of tonight’s waning gibbous moon.

The Summer Triangle is prominent on summer evenings, but now, as we drift toward autumn, we still have several months to watch this large asterism (an asterism is just a noticeable pattern of stars). This huge star pattern looms from south to overhead at mid-evening in September and early evening in October. After the moon drops out of the evening sky in mid-September, look for the glowing band of stars that we call the Milky Way to run right through the Summer Triangle.

On a dark, moonless night, you can see an edgewise view of the galactic disk - and the Dark Rift - passing right through the Summer Triangle. Photo credit: cipdatajeffb

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Great Rift: Dark area in the Milky Way

Today’s chart has you looking south to overhead on a September or October evening. If you crane your neck to look straight up, you’ll see the three bright stars forming the Summer Triangle. How can you recognize them? Well, Altair is noticeable as a bright star with two fainter stars on either side of it. Deneb lies at the top of a cross-like figure – the pattern of the cross is actually another asterism, known as the Northern Cross. This cross lies inside the Summer Triangle. And Vega is recognizable for its sapphire-blue color, and for the fact that its constellation Lyra is small and distinct in shape. Lyra consists of a little triangle, of which Vega is part, with a little parallelogram attached.

Northern Cross: Backbone of the Milky Way

Finally, if you’re looking in a dark sky, you’ll see that a rich region of the Milky Way – the edgewise view into our own galaxy – runs through the midst of the Summer Triangle. On September and October evenings, look for the Summer Triangle to shine from south to overhead, defined by Vega, Deneb and Altair. Although you can see the bright stars of the Summer Triangle on a moonlit night, you’ll need a dark sky to see the Milky Way’s luminescent band of stars. If there’s too much moonlight this evening, try again after a few more days.

Summer Triangle: Vega, Deneb, Altair