Temperature and Spectrum
Some stars are extremely hot, while others are cool. You can tell by the color of light that the stars give off. If you look at the coals in a charcoal grill, you know that the red glowing coals are cooler than the white hot ones. The same is true for stars. A blue or white star is hotter than a yellow star, which is hotter than a red star. So, if you look at the strongest color or wavelength of light emitted by the star, then you can calculate its temperature (temperature in degrees Kelvin = 3 x 106/ wavelength in nanometers). A star's spectrum can also tell you the chemical elements that are in that star because different elements (for example, hydrogen, helium, carbon, calcium) absorb light at different wavelengths.