1. How do scientists know what stars and planets are made of?
Astronomy Unit
Earth Science

2. If we can’t go to other planets and stars….
All atoms and elements plus compounds like to emit and absorb electromagnetic radiation at different wavelengths.
If you pass sunlight through a prism, the light is bent so you can see all the different colors of light that make up white light.

3. Wavelengths Each color of light has a different wavelength.
Light can act like a particle and also like a wave.
Red light has longer wavelengths than violet light (shorter wavelengths).

4. Well, what about stars?
Scientists have studied the emission and absorption spectra of different elements.
Using a spectroscope, they can analyze the light coming from a star and compare it to known spectra from elements.

5. How else can scientists use this information?
Scientists can determine whether galaxies are moving toward or away from the Milky Way.
As a galaxy moves, it shifts the wavelengths of light that are emitted.
If the galaxy is moving away from us, the spectral lines are shifted toward the red end of the spectrum (redshift). If it is moving toward us, the spectral lines are shifted toward the blue end of the spectrum (blueshift).
This is called the Doppler Effect.