The Stellar Triangle of Summer




When the Summer Triangle sinks into the west, we know summer has come to an end. While the stars of the Summer Triangle are now high overhead from northern latitudes as the sky gets dark, by late evening the Summer Triangle is setting into the west.

These three bright stars are an example of stellar variety:

– At bottom is Altair in Aquila the eagle. It’s a white main-sequence star 17 light years away, fairly nearby by stellar standards. Leslie Nielson and his crew went to Altair in the 1950s movie Forbidden Planet.

– At top right is Vega, in Lyra the harp, a hotter and more luminous blue-white star than Altair, making it appear brighter than Altair, despite Vega being farther away, at 25 light years distant. Jodi Foster went to Vega in the movie Contact.

– But the third member of the Triangle, Deneb, at top left, is an extreme star. It appears a little fainter than Vega, but looks can be deceiving. Deneb is actually a luminous supergiant star, putting out 54,000 times the energy of our Sun. Deneb is about 1,400 light years away and yet, due to its fierce output of light, appears almost as bright as Vega. Light from Deneb left that star in the 6th century. I don’t know of any movie heroes who went to Deneb. The name means “tail of the Swan,” hardly a romantic destination for space-faring adventurers.

Look toward the Summer Triangle and you are looking down the spiral arm of the Milky Way that we live in. The stars of that arm appear as a packed stellar cloud running through Cygnus the swan, the constellation that contains Deneb.

I took this shot Saturday night, from home, on what turned out to be a very clear night, once some clouds got out of the way in the early evening. This is a 4-image stack of 8-minute exposures, at f/4 with the 35mm Canon lens, a favourite of mine, on the Canon 5D MkII at ISO 800. I added in exposures taken through a soft-focus filter to give the added glows around the stars to help make the bright stars and their colours more visible.

— Alan, September 25, 2011 / Image © 2011 Alan Dyer

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