There are currently six
major terms that we use to describe stars. There are more then six ways to describe a star, but these are the most common and the most relevant to the
casual observer.
- Stellar Class
- Stellar class is determined by the surface temperature of a star.
- Class 0 - 30,000 – 60,000 K
- Class B - 10,000 – 30,000 K
- Class A - 7,500 – 10,000 K
- Class F - 6,000 – 7,500 K
- Class G - 5,000 – 6,000 K
- Class K - 3,500 – 5,000 K
- Class M - 2,000 – 3,500 K
Absolute Magnitude- Absolute magnitude is the measure of the apparent magnitude a star would have it was placed 10 parsecs from earth, and now in english. Absolute magnitude is a way of measuring how bright a star is. Since some stars are farther away from Earth then others, the way they appear in the sky (apparent magnitude) is a poor measure of how bright a star really is. Absolute magnitude is a measure of how bright a star would be if it were put 10 parsecs (32.6 light years) away from earth . A light year is the distance that a beam of light travels in a year.
Right Ascension- The first of two necessary coordinates to find a point on the celestial sphere. Right ascension tells you how far to the right (east - think longitude) a star will appear in the sky. Right ascension is measured from the vernal equinox point, which is the point the Sun occupies on the vernal equinox. The right ascension is measured in hours, minutes and seconds. Hours are equal to 15 degrees of an arc, minutes are equal to 1/60th of a degree(a minute is 1/60th of an hour), and seconds are equal to 1/3600th of a degree (a second is 1/3600th of an hour.)
Declination- The second coordinate needed to find the point on the celestial sphere. Declination tells you how far above (think latitude) a point is from the celestial equator. The celestial equator is a line that is radiated by the equator. An object directly over the north pole has a declination of +90 degrees, while an object below the south pole has a declination of -90 degrees. This is also measured in hours, minutes, and seconds.
Parallax- This one is good for visual people. Imagine a star floating out in the midst of space. Now draw a line from earth to the star, and then from the star back to the sun. You have just created a giant angle in space. The measure of this angle is the parallax of the star. If this method doesn't work, vuo suggests that you visualize the star on your fingertip. Hold your arm out and imagine that your left eye is the Earth and your right eye is the sun. The angle made by your eyes focusing on your outstretched finger is angle known as parallax. Parallax is a fun measurement. If you take the reciprocal of the parallax, that is (1 / the parallax) you will solve for the distance away from earth that the star is in parsecs (1 parsec equals 3.26 light years)
Distance- This is the simplest description, it tells you how far away from earth the star is. This distance is given in light years, which are the distance that light travels in one year. One light year equals 5,820,000,000,000 miles (or ten billion kilometers). What this means is, if you got in a jet plane, it would take you twelve hundred years to get to the nearest star. Space is big.
Example:
Wolf 359: Class: M6 | Absolute Magintude: 16.55 | Right Ascension: 10h 56m 28s | Declination: +7h 0m 42s | Parallax: .419degrees | Distance: 7.78 Lightyears