Question

astronomers can determine the chemical composition of stars by observing which of the following?
speed of rotation of the star at its equator.
wavelengths of light emitted by the star.
time the star takes to move through the night sky.
the season of the year in which the star is seen

Explanation:

Each element emits light at specific wavelengths. By analyzing the wavelengths of light emitted by a star (spectral analysis), astronomers can identify the elements present, thus determining the star's chemical composition. The other options - star's rotation speed, its movement across the sky, and the season it is seen - do not directly relate to determining chemical composition.

Answer:

Wavelengths of light emitted by the star.