Seeing Stars: The Summer Triangle 

Keith Wilson has had a lifelong interest in the night sky and has written for space and astronomy publications in the UK and USA. He lives under the dark night skies of the Isle of Gigha.

 

By Keith Wilson

 

Our summer night sky has a great signpost to spot our Milky Way galaxy this month.

 

It’s called the Summer Triangle and just like The Plough, which I described in May, it isn’t a constellation, just a pattern of stars which in this case spans several constellations and a galaxy.

 

The Summer Triangle consists of three bright stars in three separate constellations.

 

First is the star Deneb in the constellation of Cygnus the Swan.

 

The second point of the triangle is the sparkling blue-white star Vega in the constellation Lyra the Harp and to complete the triangle is Altair in the constellation Aquila the Eagle.

 

Look for the Summer Triangle on a clear August evening and, once you find it, you can watch it all summer as it shifts westwards through autumn and early winter.

 

Vega is the brightest of the three stars. From Kintyre, Vega passes almost overhead during summer evenings and it stands out really well because there are no other bright stars in the area.

 

If you look below Vega you will find Altair. A 30cm ruler, held at arm’s length, fills the gap between these two stars.

 

Look to the left of Vega for another bright star. This is Deneb. An outstretched hand at arm’s length is approximately the distance from Vega to Deneb.

 

If you are able to get well clear of light pollution under a dark starry sky on a night when the moon is absent, you will see a great band of stars passing between the Summer Triangle’s Vega and Altair.

 

The star Deneb sits in the middle of this river of stars which curves across our summer skies.

 

What you are looking at are the billions of stars in the Milky Way, our home galaxy.

 

Deneb is actually the tail of Cygnus, the swan, with the swan’s neck stretching out midway between Vega and Altair.

 

The swan’s wings, neck and tail make it look a little like a cross and so sometimes this pattern of stars is called The Northern Cross.

 

According to a 3,000-year-old Chinese legend, Vega was a weaving girl and Altair was a  boy who herded cows.

 

The two were so enamoured with each other that they forgot about their duties, so were banished to opposite sides of the barrier of the Milky Way and were allowed to meet only once a year.