What device is used to know what a star is made of and how old it is?

Astronomers use a spectroscope to determine what a star is made of and its age. A spectroscope analyzes the light emitted or absorbed by a star, revealing its spectrum, which contains distinct lines corresponding to different elements. By studying these spectral lines, scientists can identify the star's composition. Additionally, the star's age can be estimated through models of stellar evolution, often using its luminosity and temperature alongside its spectral data.