Color of Stars – What Color Are The Stars In The Sky?

(Last Updated On: August 30, 2019)

How it started?

An 11-year-old boy learning in school was very affectionate about the colors of the stars. He built his own telescope and started watching the stars. And this child changed everything with his telescope and his genius mind which set the basics of our science. His name was Karl Schwarzschild. He solved so many areas of the science which were only imaginations. He solved the general relativity, quantum physics, colors of stars and showed the proofs of black holes.

Karl Schwarzschild - color of stars
Karl Schwarzschild (1873-1916)

Electromagnetic Spectrum

The color of stars depend upon the surface temperature. The colors we see from the earth comes from the mixing of various light waves of different wavelengths. Already light coming from the stars consists of gamma rays, x-rays, ultraviolet, visible light, infrared and radio waves. And the white visible light is further mixing of red, orange, yellow, green, blue and violet colors.

Also Read: Life of Stars – Birth To Death

Electromagnetic Spectrum with their wavelengths
Electromagnetic Spectrum with their wavelengths (Source – Cyber Physics)

What is the color of stars and why do stars have colors?

We consider the blue color is cold and the red color is hot but in reality, it’s opposite. Red color is very much cooler than the blue color. For the instance consider an iron rod and go on heating, at first it becomes red hot but as we further increase the temperature it goes on becoming yellow to white and at last in its molecular or in 4th state of matter, plasma, its color becomes blue. This pattern is applicable in the star’s color also.

Also Read: Time Crystals – The Sixth State of Matter

Superhot stars seem blue as they emit a high amount of energy which moves them in the blue side of the spectrum, whereas the cold stars seem red as they release low energy hence residing towards red color (refer above image for the relationship between energy, wavelengths, and colors). But normal stars emit energy through every part of the spectrum they look like yellowish-white in color. But in general, blue stars are very hot and red are cold (Here cold means in the temperature range of stars not normal range).


Scientists have made seven parts as per the color of stars and their temperatures as shown in the above image. This is known as ‘spectral class’. The classes are O, B, A, F, G, K, M respectively. Stars are grouped according to temperature, with the massive, very young and energetic Class O stars boasting surface temperatures above 30,000 K. Class B stars have surface 3 temperature of about 30000 K to 10000 K. Under Class A those stars come whose surface temperature is 10000 K to 7500 K. Class F consists of the stars having surface temperature 7500 K to 6000 K. Class G consists of stars having surface temperature 6000 K to 4900 K. Class K consists of stars having surface temperature 4900 K to 3500 K. While the less massive, typically older Class M stars exhibit temperatures less than 3,500 K.

Hertzsprung-Russell diagram - color of stars
Hertzsprung-Russell diagram


This classification is done based on the variation in the luminosity of stars. Because luminosity is
proportional to temperature to the fourth power, the large variation in stellar temperatures produces
an even vaster variation in stellar luminosity. Because the luminosity depends on a high power of
the stellar mass, high mass luminous stars have much shorter lifetimes. The most luminous stars
are always young stars, no more than a few million years for the most extreme.


Luminosity of stars
Luminosity of stars
Empirical mass-luminosity relationship
Empirical mass-luminosity relationship

Our sun is a Class G star. There is further classification also based on magnitude apparent and absolute. And those 7 classes are divided into 10 further classes as O1, O2…… based on their temperature itself. There is another classification based on their lifetime – Supergiants, Bright giants, Giants, Sub giants, Dwarf and White Dwarf.

These are the various color of stars. As we see upon the sky in dark we may not see it by our naked eyes but if we try to see it with our passion and telescopes we can see that the dark skies also play the colors.

Also Read: A New State Of Matter You Might Have Never Heard About

Bhalchandra Ravindra Yalamali

Bhalchandra Ravindra Yalamali

He is an astrophysics lover. He loves to explore the field of astrophysics.

One thought on “Color of Stars – What Color Are The Stars In The Sky?

  • August 27, 2019 at 10:48 pm

    I love physics …I want to do something new in physics in future.


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