Light and Spectra: Background

Light can tell us a great deal about astronomical objects. In fact, it can often tell us what the objects are made of! In this portion of the lab you'll discover how scientists use spectrometers to figure out what distant stars are made of.

Light actually comes in waves. The length of the wave determines the color of the light. When you look at white light, you're actually looking at lots of different colors of light, all mixed together! We will use a tool called a spectrometer to figure out the different wavelengths of the light we are looking at. The spectrometer contains a diffraction grating, which splits the light into different wavelengths. Our spectrometers are pretty simplistic, but conceptually are the same as spectrometers in the most advanced telescopes.

One nice feature of the Universe is that different elements (hydrogen, helium, oxygen, uranium, ...) like to emit different wavelengths (colors) of light. Each element has a unique set of specific colors. So if we have different elements in a lab, and we measure the specific wavelengths for those elements, we can actually identify those same elements in the farthest galaxies, just by splitting apart the light from the galaxy!.

The reason each element has this unique "fingerprint" is that the atoms of each element have small particles called electrons, which can jump between levels where they have different energies. When they jump down, they give off a certain amount of light. The farther they jump, the shorter the light waves are (this means they are more blue). But each element has a different set of levels, and so each gives off its own specific set of colors.