ASTR 1514 1st Edition Lecture 23Measuring the Stars Temperatures Chapter 10.2Atoms and Energy Levels- Blue stars are hot- Red stars are cooler- Atoms have dense nucleus of protons and neutrons- Electrons surround nucleus in a cloud- Each atom has a unique set of energies, Energy levels of a particular atom identify an atom or ion - Permitted orbits: Electron configurations that are allowed in an atom- Energy Levels: The energies required for the permitted orbits- Ground state: The electron is in its lowest energy level.- Excited state: Electron is in higher energy levelExcited Atom- Electrons like to be in the lowest energy state.- It takes energy to raise the electron to a higher state- It must emit or absorb exactly the right amount of energy for it to go from one energy level to another- Light photon contain energy (E=hf)- So absorption of light can excite atoms. - Certain wavelengths will promote the electron to a higher energy level. Emision: Atom emit a photon and the electron drops to a lower energy state, losing energy. Photons energy is equal to the energy difference between two levels. Two ways to excite and atom1. Absorption of a photon – (Must have energy equal to one of the energy levels)2. Collisions – A free elctronThe photosphere of a star emits as a blackbodySome light from the star is absorbed by atoms in the stars atmosphere. Stellar Classification OBAFGKM – O (Hotter stars) – M (Cooler stars) -Hotter stars: Weak absorption by hydrogen and helium (Type O)-Middle: Strong hydrogen absorption (Type A)-Cool stars: Many different heavy elements or molecules (Type M)Measuring the size of stars- Knowing the temperature and luminosity of a star can help us determine the radius of a star- (Larger and hotter stars are more luminous)- Stars have radii measuring 1% of the sun’s radius to 1000 times it’s
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