Stars are one of the most timeless furnishings of our universe. Age after age they have been permanent fixtures in our sky, being the base for countless religions, wishes, and art. Yet most people do not realize exactly what these sparkling lights are, and how different each is. In Astronomy, stars are the snowflakes of the universe: each has unique characteristics making it an individual.
Many stars look uniform. All stars sparkle (because of the interference of our atmosphere not because they really sparkle), and the differences we notice with the naked eye are not usually due to differences in the star, but to factors such as distance and light pollution and interference. To really see the distinguishing characteristics it is really necessary to use a telescope, preferably the high powered variety.
Looking through telescopes, as well as using other means to analyze stars such as spectro-analysis, we are able to classify stars using several criteria. Typically, stars are distinguished by using a scale of 7 letters that describe their spectra (or the elements they absorb).
The 7 classifications in decreasing order of temperature are: O, B, A, F, G, K, M. An easy way to remember this order is the famous pneumonic, “Oh, Be A Fine Girl Kiss Me.”
Each of these letters corresponds to an approximate surface temperature range. “O” for an example is over 25,000 Kelvin’s, and “M” is under 3,500 Kelvin’s.
The Hertzsrung-Russel Diagram is an often used diagram that plots star types against their luminosity.
Another part of the classification of stars is their sequence. Main sequence, or young stars, are the most common making up about 90 percent of all stars. This group of stars derrive their energy from Nuclear Fission converting Hydrogen to Helium. The hotter these stars are, the brighter they are. The sun is a typical Main Sequence star.
The next group are Dwarf Stars which are small, and very bright. The best example is our sun which is a dwarf.
– A Yellow dwarf is a main sequence star such as our sun.
– A Red Dwarf is a cooler main sequence star that is the most common star in the universe.
As stars age, they become giants and supergiants. This is because their matter becomes looser and spreads causing it to expand in size.
-A red giant is a very old star that is roughly 100 times as big as its original size, and frequently orange colored. An example of this star is the nearby Betelgeuse.
Blue Giants are gigantic and super hot stars.
Supergiants are the biggest stars known; some are as big as our entire solar system.
Stars that are about dead and very faint include stars such as White Dwarfs, Neutron Stars, and Pulsars.
There is much variance within these classifications and groups. Sometimes it’s hard to strictly put a star in one category, and eventually, they often change color with changing temperatures etc.
