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The Summer Triangle
updated: Oct 12, 2013, 2:00 PM
By Chuck McPartlin
Summer is gone, but there is a reminder of summer in Santa Barbara's evening
skies that will be with us for the next month or so. About an hour after sunset,
step outside and face southwest. Look for three bright stars forming a large
triangle in the darkening sky. This is the Summer Triangle, so named because it
decorates the night sky overhead from late spring until early autumn.
The star at the lower left, or southern end of the triangle is Altair. At about
17 light years away, this is the closest star to the Sun that you can see on an October evening from Santa Barbara without a telescope or binoculars. It is
about 11 times more luminous than the Sun. It is a very rapid rotator, about once in nine hours, so it is distorted into an oblate shape, which has actually
been imaged with an optical interferometer telescope array.
The star to the right, or western vertex of the triangle is Vega, still pretty close at a distance of about 25 light years. Vega is also
a movie star - it was the first star to be photographed, in 1850, and was the source of the signals in the movie Contact. It is about 40 times more luminous
than the Sun, and has a disk of dusty debris around it, perhaps like our asteroid belt. In about 12,000 years, precession of the Earth's rotational axis will
make Vega our north star.
The star at the top, or eastern corner of the triangle is Deneb, the farthest away at an estimated 2,600 light years. It's big and
bright, with a radius of about 200 times that of the Sun, and a luminosity about 160,000 times greater. Blue supergiant stars like Deneb only last a couple of
million years, so enjoy the sight while you can! Deneb will also be our pole star one day, in about 7,800 years.
The Summer Triangle is an asterism made up of parts of several constellations. The three most prominent ones incorporate the
bright corner stars.
Altair is the eye of Aquila the Eagle. Some people also see a Bat Ray, or an Umbrella. OK, that bottom star is not officially part of
Aquila, but it makes the umbrella
handle more plausible.
Vega is part of Lyra the Harp, made by Orpheus from a tortoise shell. Your guess is as good as mine on what it really looks like.
Deneb is the tail of Cygnus the Swan, flying south along the band of the Milky Way. On a good night you can see the dark rifts
caused by clouds of opaque gas and dust concentrated in the plane of our galaxy.
Another interesting star is Albireo, the beak of the swan. It looks like a single dim star to your eye, but a telescope view reveals a
binary system, with a blue star and a yellow star, so it's sometimes called a Cub Scout star. What's really cool is that it is about 400 light years away, so the
light you see left there when Galileo was looking at the sky.
Sky images from Starry Night Pro.
Links for a Cloudy Evening
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