What do astronomers use to determine the temperature of a star by using what instrument?

Astronomers determine the temperature of a star primarily through its spectrum using a spectroscope. By analyzing the spectrum of light emitted by the star, they can identify the absorption lines, which correspond to different elements and their ionization states. The presence and intensity of these lines allow astronomers to estimate the star's effective temperature using the principles of blackbody radiation and models of stellar atmospheres. This method helps classify stars and understand their physical properties.