Question

Explain how we use a spectrometer to help us determine what stars and planets are made of?

Answer 1

A spectrometer measure the electromagnetic spectrum of the light intensity radiated from the stars. so the intensity coming from the star, is made up of light at different frequencies(or wavelengths) and they all are of varying intensities.
So, in this way, by analysing the spectrum, one can observe whether a star is radiating its maximum intensity at what frequency.
'Hotter' stars radiate most at a higher frequency than relatively 'cooler' stars.

If we know the distance to the star, by looking at the intensity, we can ascertain the 'effective temperature' of a star. which for most practical purposes is the surface temperature of the star.
So just by analyzing the light from the star, we can know the star's surface temperature !
once, we know the surface temperature, we can categorize the star i.e. find out what stage of evolution the star is in. This means whether its a young star, old star, red giant, sun-like, white dwarft etc.

Answer 2

thank you sorry i replied late i understand so much better now