‘The Summer Triangle’ can be easily found in the evening sky over the summer months in the northern hemisphere.
It is an asterism made up of the brightest stars in the constellations of Lyra, Cygnus and Aquila.
An asterism is a pattern of stars in our night sky that can be made up of stars in one constellation (such as ‘the Plough’ in Ursa Major) or stars from several constellations. Generally, asterisms are useful for finding other objects in the night sky, or their appearance signals the changing seasons.
The bright, 1st magnitude stars forming the Summer Triangle are Vega, Deneb and Altair. Given their brightness, it is often possible to view the Summer Triangle even from within light-polluted towns or cities.
In darker skies, where there are many more visible stars, a technique for establishing you’ve found the right stars is to slowly close your eyes. As you get close to having your eyes closed only the brightest stars will remain visible – the three brightest of which (assuming you’re looking in the right direction!) will be Vega, Deneb and Altair.
The giant triangle they form lies through the familiar band of the Milky Way and is visible overhead through midnight in mid-lattitude locations in the northern hemisphere through much of summer.
The image below traces out the Summer Triangle in the night sky:
Lyra is the harp once played by the great mythological Greek musician, Orpheus. The bright star Vega is the fifth brightest star in the sky and lies some 25 light years away from us.
Deneb by contrast is in the region of 1500 light years from us and is a blue-white supergiant – probably around 20 times as massive as our Sun. The star is the brightest in the constellation of Cygnus: depicted as a swan gracefully gliding through the Milky Way.
Aquila the eagle was the carrier of Zeus’s thunderbolts. Altair is its brightest star and about 17 light years away and the 12th brightest in our sky.
With each of the 3 stars forming the Summer Triangle within the top 20 brightest stars in the sky, this is a great and relatively easy asterism to spot.