How Do Spectrographs Help Astronomers Classify Stars

how do spectrographs help astronomers classify stars

So you’ve been training to be an astronomer for some time now. You know how stars form, how they evolve over different stages of their lives, and even how they eventually die. But still, there’s one thing that’s been bugging you: how do spectrographs help astronomers classify stars? What are spectrographs, and why do we need them to study stars? Let’s find out in this article.


A spectrograph is a device that breaks down the light from a star or other source of electromagnetic radiation (such as a supernova) into a spectrum. That spectrum is then analyzed to determine the various properties of the light source. You may be wondering how this works.

The short answer is that the device uses a prism or a grating to break down the light from the star or other source into its wavelengths. A spectrum is a graph plotting the amount of electromagnetic radiation at each wavelength.

In addition to the overall amounts of radiation found in the spectra, astronomers can also use the Doppler effect to determine the velocities of astronomical objects. So, a spectrograph is a device that can break down light and determine the velocities of astronomical objects.


You might have noticed that astronomers have a way of classifying stars. This is because stars have different properties, and knowing these properties helps astronomers better understand stars. For example, by knowing how much light a star emits, astronomers can understand how large it is.

The same is true for temperature, chemical composition, and age. If you want to understand the lifetime of a star, you need to know its rotation rate, luminosity, and its chemical composition. The only way to find out these properties is by classifying the stars. Spectrographs help with this.

Stellar Mass Classification Using Spectrographs

Let’s start with stellar mass classification using spectrographs. Stellar mass is the amount of matter in a star, and it determines how long a star will live. Hence, knowing the stellar masses of stars can help astronomers better understand how long the stars will live.

A star’s luminosity determines stellar mass. Hence, the only way to determine the stellar mass of a star is by knowing the star’s luminosity. Luminosity is the amount of energy emitted by a star per second. If a star is moving away from us, its light will be shifted towards the red end of the spectrum.

The spectrum of a star depends on the temperature inside the star. The hotter the star, the more blue the light. The cooler the star, the more red the light. A star’s spectrum can be read like a fingerprint. Astronomers have cataloged and studied the spectra of different stars, and they have created stellar spectral classifications.

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