Space Rumors

Have you ever noticed the color of the stars?The light they put out varies some what in color from one star to another. In some cases you can see this difference easily. For example, in the constellation Orion, which is visible in the evening around December, the two brightest stars have distinct colors: Betelgeuse, in the north east corner, is red; while Rigel, in the south west corner, emits a blue-white light. The stars have a whole range of colors, from red to orange, yellow, white and finally blue-white.

These color differences tell us how hot the star is. Every warm body emits light and heat(these are two forms of electromagnetic radiation), whether it is a star or an incandescent light bulb. A light bulb filament, heated by electric current, emits radiation, a small part of which is visible light. If, for example, the temperature of the filament goes down, then the light it emits turns yellowish or even reddish. If, on the other hand, the temperature of the filament rises, the light is not only more intense but also whiter and more bluish. The color of the light emitted lets us know the temperature of the body that is emitting it.

In this way, we know that the material the stars are made of is so hot that it takes the form of a gas: stars are huge balls of gas, mostly of hydrogen. This gas is extremely hot, and because of its high temperature it emits light and heat. The color of the light tells us the temperature of the stars surface.

Astronomers measure star temperatures in a metric unit known as the kelvin. One kelvin equals exactly 1 Celsius degree (1.8 Fahrenheit degree), but the Kelvin and Celsius scales start at different points. The Kelvin scale starts at -273.15 degrees C. Therefore, a temperature of 0 K equals -273.15 degrees C, or -459.67 degrees F. A temperature of 0 degrees C (32 degrees F) equals 273.15 K.

Dark red stars have surface temperatures of about 2500 K. The surface temperature of a bright red star is approximately 3500 K; that of the sun and other yellow stars, roughly 5500 K. Blue stars range from about 10,000 to 50,000 K in surface temperature. Although a star appears to the unaided eye to have a single color, it actually emits a broad spectrum (band) of colors. You can see that starlight consists of many colors by using a prism to separate and spread the colors of the light of the sun, a yellow star. The visible spectrum includes all the colors of the rainbow. These colors range from red, produced by the photons (particles of light) with the least energy; to violet, produced by the most energetic photons.