Question

how do spectrographs help astronomers classify stars?
they determine the size of stars.
they evaluate the color of stars.
they measure the brightness of stars.
they analyze the composition of stars.

Explanation:

Spectrographs work by splitting light into its component wavelengths (a spectrum). Different elements in a star emit or absorb light at specific wavelengths. By analyzing the spectrum (the pattern of lines in the spectrum), astronomers can identify which elements are present in the star. This analysis of the composition helps in classifying stars. For example, stars with different chemical compositions (e.g., different amounts of hydrogen, helium, heavier elements) will have different spectral features.

Answer:

They analyze the composition of stars.