Ultraviolet energy from the brilliant star Gamma Cassiopeiae, at top left, is eroding a nearby cloud of interstellar gas, limiting the birth of new stars. Gamma Cas emits most of its energy in the ultraviolet. If you include the UV with other wavelengths of light, Gamma Cas is roughly 65,000 times brighter than the Sun. It forms the middle point of W-shaped Cassiopeia, which is in the northeast on August evenings. [Tom Bash and John Fox/Adam Block/NOAO/AURA/NSF]
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The constellation Cassiopeia circles up across the northeastern sky this evening. The queen’s brightest stars form a letter W, making the constellation quite easy to find. All five of the stars in that pattern are much bigger, heavier, and brighter than the Sun. And the most impressive of them all is the one in the middle of the W.
To the eye alone, Gamma Cassiopeia is the third-brightest of the five. In part, that’s because the star is about 550 light-years away — a good bit farther than the other stars of the W. And in part, it’s because our eyes aren’t sensitive to most of the star’s energy.
The surface of Gamma Cas is tens of thousands of degrees hotter than the surface of the Sun. To the eye alone, such stars look white or blue-white. But most of their light is in the form of ultraviolet radiation. So while Gamma Cas shines about 5,000 times brighter than the Sun at visible wavelengths, when you add in the ultraviolet, it’s 65,000 times brighter than the Sun.
How bright the star looks actually varies by quite a bit. In fact, in 1937 Gamma Cas appeared almost three times brighter than it is now, making it by far the brightest star in all of Cassiopeia. But the star expels a lot of gas into space, forming a doughnut-shaped cloud around the star. Depending on the viewing angle and other factors, the cloud can block some of the star’s light. And it’s doing so right now — dimming the luster of this impressive star.
Script by Damond Benningfield, Copyright 2013