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Light is a form of energy that travels as a wave.
The two primary characteristics of any wave are wavelength and frequency.
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For visible light, wavelength & frequency determine color. The longest wavelength is red and the shortest is blue with the other colors caused by intermediate wavelengths.
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A very long wavelength has a very low energy.
A very short wavelength has a very high energy.
LOW ENERGY
HIGH ENERGY
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How is light made and what can it tell us about distant objects?
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Every atom* has electrons. These electrons orbit* the nucleus at different energy levels.
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When a photon of light strikes an electron, the electron absorbs the energy and jumps up to a higher energy level.
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Astronomers use these energy levels to identify the atoms that make up distant stars and other objects.
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Hydrogen | |
Energy level (n) | Energy / eV |
1 | -13.58 |
2 | -3.39 |
3 | -1.51 |
4 | -0.85 |
5 | -0.54 |
Using hydrogen as our example, note the different energies associated with the electron energy levels for hydrogen.
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When an electron “falls” in a hydrogen atom, the light given off has a specific energy depending on how far it fell.
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When we see light from a distant star, we measure its frequency.
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When we know the light’s frequency, we can find its energy from the Planck equation:
E = hf
E – energy
f – frequency
h – Planck’s constant
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When we know the light’s energy, we know what element it came from because the energy levels of each element are unique.
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An electron can go between many different levels, so every atom gives off light ant several wavelengths at once.
NOTE: Each line is a different “color”.
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These different colors are called an element’s SPECTRUM�aka Spectral lines.
When you observe a certain set of spectral lines, you know what a star is made of.
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These different colors are called an element’s SPECTRUM�aka Spectral lines.
When you observe a certain set of spectral lines, you know what a star is made of.
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Spectrometer: A device that very precisely measures the wavelengths of light. It can distinguish light emitted by different atoms.
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For example, we know that Jupiter is made of mostly H, and that Venus’ atmosphere is made of CO2 with traces of sulfuric acid.
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There are many different kinds of telescopes that are able to detect different parts of the EM spectrum. These wavelengths can then be interpreted graphically or translated into colors we are able to see.