Hello! I’m Karl Hricko for the United Astronomy Clubs of NJ, and the National Space Society bringing you the November Astronomy Update for the WNTI listening area.
Next time, look closely at the stars. Can you see their colors? You should be able to see red, orange, yellow, and blue stars. Generally, the color will give you the surface temperature and the relative age of the star. Red would indicate a cooler and older giant star, while blue is the hottest and youngest. Rigel is a hot blue giant star in Orion, and Antares is a cool older red giant in Scorpius. Our Sun is considered to be a yellow dwarf star of medium temperature and age.
While you can figure out the relative temperature of a star by its color, astronomers can calculate the actual temperature by using the star’s apparent brightness or magnitude. What we see as the brightness of a star depends on its distance. The farther a star, the dimmer it appears. Astronomers compute the distance and then convert it from apparent to absolute magnitude. Knowing this, they can determine the star’s temperature.