Why Are Stars Different Colors?

Space is vast, very cold, very scary but also beautiful, and it is full of objects that emit light/wavelengths of electromagnetic radiation in all the colors of the spectrum. One of these objects is Stars. Stars are massive, very hot and they come in a variety of different sizes and colors, why is this?

Why are Stars Different Colors?

Why Are Stars Different Colors?

One reason why stars are different colors is due to their temperature. Scientists believe that cooler stars emit the color Red, and the hottest stars in temperature emit either white or blue light. Star colors from coolest to hottest. Red, Orange, Yellow, Blue sometimes White. The hottest stars also tend to be the largest.

Approximate Star Temperature by Color

  • Red – 3000 Kelvin – 2700 Celsius
  • Orange – 4500 Kelvin – 4200 Celsius
  • Yellow – 6000 Kelvin – 5700 Celsius
  • Blue/White – 25000 + Kelvin – 24000 + Celsius

The star in the center of our own solar system, (The Sun) is considered a yellow dwarf star. However our sun may seem white to the naked eye. Stars emit what is considered a peak wavelength or color, this is its primary color, however it also emits all the wavelengths or colors of the spectrum, and when you combine these wavelengths in light it creates the color white. This is how white is created in color devices such as your TVs, tablets and smart phones, which use the Additive RGB primary color model.

You can see all of the wavelengths/colors, that the sun emits when the sun is shining and when it rains. The water separates the colors into the 7 colors of the visible spectrum, which can be seen in the colors of the rainbow.

The color of stars do change over time as they go through different periods of activity including cooling and warming. It does seem strange that the cooler stars are red, and the hottest stars are more of a bluish color. Back on earth red is a warm color and associated with heat for obvious reasons, while blue is a primary cool color often associated with winter and ice. Why is this?

As a stars temperature increases, the wavelengths that the star emits get shorter, and the shortest wavelength is that of the color blue. This is why the hottest stars appear blue.

Star Composition

Temperature is not the only factor that determines the color or combination of wavelengths that stars emit. A Stars composition is made up of various different elements, and these elements also dictate a stars color. These primary elements are helium and hydrogen, plus a few other less prominent elements.

The balance of these elements or composition will differ from Star to Star with no two Star being exactly the same. This differing composition is responsible for differences in temperature, therefore the light/wavelengths it emits.  

So the color of a star can tell scientists roughly the temperature of a star, and also the abundance of elements and the atmospheric conditions of a particular star.

Phases of a Star

Stars also go through different phases, which is part of a stars life cycle. Our sun is currently in its main sequence phase, when that phase ends, scientists believe it will become a red giant, which will indeed be red in color. Eventually it will collapse into a white dwarf, which is its final phase. If the star is large enough it will collapse into a neutron star, which will also be white. When the most massive stars collapse they form black holes. The gravity of a black hole is so strong that even light doesn’t escape, they don’t emit any wavelengths/light, therefore they’re black.   

Doppler Effect

There is also another factor which can alter the appearance and color of a star, this is the distance we are from a particular star. Light waves can change, either increase or decrease depending on the distance, this is known as the (Doppler Effect).

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