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• Generated by processes at the atomic level
• Changes in the way parts of an atom interact and move
• Forms of electromagnetic radiation are described by the electromagnetic spectrum
• Low energy --> low frequency
• High energy --> high frequency
• Particles are photons
• Types of radiation emitted by astronomical objects is determined by their temperature
Type of Radiation Wavelength Range (nm) Radiated by Objects at This Temperature Typical Sources
Gamma Rays Less than 0.01 More than $10^8$ K Nuclear reactions
X-rays 0.01-20 $10^6-10^8$ K Gas clusters in galaxies, supernova remnants, solar corona
Ultraviolet Rays 20-400 $10^4-10^6$ K Supernova remnants, very hot stars
Visible light 400-700 $10^3-10^4$ K Stars
Infrared $10^3-10^6$ $10-10^3$ K Cool clouds of dust and gas, planets, moons
Microwaves $10^6-10^9$ Less than 10 K Active galaxies, pulsars, cosmic background radiation
Radio Waves More than $10^9$ Less than 10 K Supernova remnants, pulsars, cold gas