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Physical Science Workshop: Astronomy Applications of Light & Color Applications of Light to Astronomy Applications: Based on the spectrum of a celestial object (planet, star, nebula) we can learn: o How hot it is (surface temperature) o What it is made of (chemical composition) o How fast it is moving relative to Earth (towards or away) Continuous Emission: o Continuous emission from thermal Blackbody radiation allows us to estimate the surface temperature e.g. infrared emission of a planet (asteroid, etc.) For stars (like the Sun), we use the visible spectrum! Emission Lines: o Observing which wavelengths are emitted tells you about the chemical composition of a thin, excited gas (e.g. hot upper atmosphere of a planet, comet tail, Orion Nebula) Absorption Lines: o Observing which wavelengths are missing after reflection tells you about the composition of the reflecting surface! o Observing which wavelengths are missing after passing through material (e.g. atmosphere of a planet or star) tells you about that material Most of the stuff in the universe is hydrogen (~71% by mass, ~91% by number of atoms) and helium (~27% by mass, ~9% by number of atoms) Doppler Effect: o Observing the shift in a spectrum (emission-line or absorption-line) tells you how fast the object is moving towards / away from the Earth Binary Stars: orbits Detecting planets around other stars Spin of asteroids, Venus Expansion of universe (motions of distant galaxies) Dark matter (motions of stars inside galaxies) S. Sallmen Astronomy Applications