A color index of a star is the difference in the magnitudes measured at any two wavelengths and is one way that astronomers measure and express the temperature of stars. … We can measure its detailed chemical composition as well as the pressure in its atmosphere. From the pressure, we get clues about its size.

What are different ways astronomers use starlight to study stars?

From spectral lines astronomers can determine not only the element, but the temperature and density of that element in the star. The spectral line also can tell us about any magnetic field of the star. The width of the line can tell us how fast the material is moving. We can learn about winds in stars from this.

What is the name of device that astronomers use to analyze starlight?

A spectrograph is an instrument used to obtain and record an astronomical spectrum. The spectrograph splits or disperses the light from an object into its component wavelengths so that it can be recorded then analysed.