When light goes through a prism, it separates into many colors. This band of colors is called a spectrum. A rainbow is an example of a spectrum: red, orange, yellow, green, blue, violet.
The interior of a star produces a continuous spectrum of light, like a rainbow. Cooler gases in the outer layers of the star absorb certain wavelengths of light, causing dark lines to appear in the spectrum.
The resulting absorption spectrum can tell astronomers a great deal about the star. It's like a finger print or bar code that tells information about the star's color, composition, and surface temperature.
Look at Star 1's absorption spectrum:
How many lines do you see in the spectrum?
Compare the neutral Hydrogen spectrum (bottom) to the Star spectrum (top). Do some of the lines on the two spectra match up?
Compare the neutral Helium spectrum (bottom) to the Star spectrum. Do some lines match?
Based on this information, does Star 1 contain neutral hydrogen and helium?
