What does a spectrograph help astronomers to determine?

Hint: A spectrograph is a device that has the capability of separating the incident light into a spectrum of different wavelengths or different frequencies. It allows us to know more about the chemical composition of the incoming light. Basically, a spectrograph is an instrument that can be used for dispersion of light into a spectrum.

Complete step-by-step answer:
The spectrograph separates the incoming light into a spectrum; hence astronomers use spectrographs to disperse the light emitted by the stars and find out various important results on its basis. The astronomers are able to find out the chemical composition of the stars along with the physical changes that happen in them. Also, the benefits of using a spectrograph do not end here, it is used to determine the temperatures of a particular element of the stars and even its density in the star. This instrument also helps astronomers to find out the magnetic fields of the star along with the speed of the star with which they are moving. Deflection in the spectrum also helps the astronomers to determine whether that particular star is being affected by the presence of some other star or not. Astronomers are even able to determine the mass and size of a particular star.

Note: A spectrograph works by splitting up the incident light into its component wavelengths. The first step of using a spectrograph to collect information about a particular star is to collect light rays from that particular star which come from a telescope and then fall on the tiny opening of the spectrograph.