The Reddest of Red Stars by Vincent S. Foster Some stars will make you see red. They are carbon stars, a unique type of variable star, that accumulate soot in their upper atmosphere that scatters light near the blue end of the spectrum. What we are left to see is the red component of a star's light. As carbon particles accumulate, the star's brightness decreases and it becomes even redder. Eventually, the carbon absorbs enough radiation to escape the star, and the cycle starts all over again. Novice observers are often disappointed because they can't see the rainbow of colors that appear in celestial photos taken by the Hubble Telescope. This is because the human eye's color sensors do not work well in low light conditions. So why can we see the color of carbon stars, but not that of most other celestial objects? Because their light is bright and concentrated in one point rather than being scattered like nebulae and galaxies. Point binoculars or a small telescope at a carbon star and you'll see its color even more clearly. This is because the telescope will collect much more light than the eye and will help stimulate the color receptors. Although carbon stars are the reddest of the red stars, there are varying levels of red in these stars. Astronomers determine the redness of a star through observation and simple calculations. They measure the star's magnitude through blue (B) and visual (V) filters. They then subtract the visual magnitude from the blue. This leaves a designated BV number called the color index. The more positive the color index, the redder the star. For example, if a star has a blue magnitude of 5 and a visual magnitude of 3, then it has a color index of 2. Color indices range from about -0.5 for the bluest stars t..... . in the center of the card ...... orite with a color index of 4.4, which makes it a red star of great visual impact. Its magnitude varies between 7.8 and 9.3 over a period of 369 days. If you want to observe more carbon stars, visit the website of the Saguaro Astronomy Club in the United States, which maintains a database containing 334 red stars. Go to www.saguaroastro.org The Astronomical League in the United States also has a list of 100 carbon stars as part of its Carbon Star Observing Program. It can be downloaded from www.astroleague.org Carbon stars will delight your eyes and help you sharpen your observation skills. If you keep a log of observations, you might exhaust your thesaurus looking for different ways to say "red." One thing is for sure, though. Looking at these red stars won't make you feel sad.ENDWord Count: 1,544Vincent S. Foster37 Brigantine Blvd.Waretown, NJ 08758USATel: 609-488-5898Email: [email protected]