It’s almost the solstice. Here in the Northern Hemisphere, the days are long, the sun is at its most intense for the year, and the weather is warm – but not as warm as it will be later this summer. And the summer sky is with us, too. The famous asterism known as the Summer Triangle is now ascending in the eastern sky on these June evenings.
The Summer Triangle is not a constellation. Instead, this pattern consists of three bright stars in three separate constellations – Deneb in the constellation Cygnus the Swan, Vega in the constellation Lyra the Harp, and Altair in the constellation Aquila the Eagle. Learn to recognize the Summer Triangle asterism now, and you can watch it all summer as it shifts higher in the east, then finally appears high overhead in the late northern summer and early northern autumn sky.
An asterism isn’t the same thing as a constellation, by the way. Constellations generally come to us from ancient times. In the 1930′s, the boundaries of 88 constellations were officially drawn by the International Astronomical Union.
On the other hand, asterisms are whatever you want them to be. They’re just patterns on the sky’s dome. You can also make up your own asterisms, in much the same way you can recognize shapes in puffy clouds on a summer day.
But some asterisms are so obvious that they’re recognized around the world. The Summer Triangle – a large triangular pattern consisting of three bright stars in three different constellations – is one of these. The Summer Triangle appears in the east at nightfall on June evenings, swings high overhead in the wee hours after midnight and sits rather high in the west at daybreak.