“Color of the Stars-what does it indicate?”

Tiny stars in the night sky are the massive celestial objects composed of hot gases, hence they resemble thermal radiators. There exists a relationship between the mass of a star,its luminosity, and color, which is applicable only for stars burning hydrogen in the core during the prime of their lives.Their color depends upon their temperature. Hotter stars appear to be blue, medium-hot appear white and cooler stars appear red.

Hot stars have temperatures around 60,000 kelvin while cooler stars have temperature around 3000 kelvin.

Stars are classified into different categories: O, B ,A ,F, G, K ,M. This is the Harvard Classification System,made according to the temperature of the atmosphere of the star . O-type stars are hotter than B-type stars, B-type stars are hotter than A-type stars and so on.

A blue star doesn't only emit blue light, neither does a red star .They emit visible light of all colors to some degree.But, we usually specify a blue star or a red star just because it is the dominant color in the peak spectrum emitted by the hot glowing gaseous mass. There are also “green” stars that appear “white” to our eyes. This can be proved from the fact that if we pass the light emitted by a white star through a prism , we will find all the colors being spread out ,including green color.

Bluer stars are brighter because they are very huge as compared to stars of other colors and burn faster (thus they are hotter) than the smaller stars of other colors(red, yellow, green). The O-type blue stars are 30–50 times larger than the yellow-white stars. Our sun is a yellow-white star. But O-type stars burn a million times brighter , so they have very short lifetimes which is a few million years , after which they die in spectacular supernova explosions( The brilliant point of light in the explosion of a star that has reached the end of its life, is called as a supernova); whereas cooler and less massive K-Type and M-type stars burn steadily for billions of years. Young and middle-aged M-type stars are small, faint and long-lived. But as stars age and start burning heavier elements in the core, bluish O and B-type stars, for example, evolve briefly into immensely bright M-type red stars known as red super-giants.

It is known that around 88% stars in the universe are of K and M-type.Middle-weighted stars like our Sun comes under the G-type stars which comprises just 8% of all knows stars. O-Type star is the rare variety of star available in the universe.