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Astro Study Guide - Final

# Astro Study Guide - Final - CHAPTER 17 A star's parallax...

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CHAPTER 17 A star’s parallax can be used to calculate its distance with the equation: d = 1/p where d is the distance in parsecs and p is the parallax in arcsecs the inverse square law can be used to relate apparent brightness and luminosity with the equation: b(brightness) = L (luminosity in W) / 4 x pi x d(distance in M)^2 to get a stars luminosity or distance in relation to the sun with the inverse square law use: L/L of sun = (d/d to sun)^2 x (b/b of sun) the wavelength at which a star’s blackbody spectrum peaks can be used to estimate its surface temperature: T(K) = 0.0029/ wavelength max using this equation show that reds stars are cooler and blue stars are hotter. In the case of hydrogen, the absorption lines of this element are caused by the photons from the light source of certain energies that excite the electrons in hydrogen atoms to higher energy levels. When a hydrogen atom absorbs a photon particle of the right amount of energy, its electron travels from the ground state to a higher, more excited energy level, this is called a Balmer transition. The Hertz sprung-Russell diagram or H-R chart is a catalog of stars graphed based on their intrinsic luminosity (derived from the inverse square law) vs. surface temperature.

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Due to the inverse square law, if two stars have the same surface temperature, but difference luminosities, the star with the higher luminosity will have a larger radius, indicating its red giant phase. The greater the mass of a main sequence star, greater its luminosity, surface temperature, and radius. the brightness of a Cepheid variable star fluctuates over the course of a few days, making them useful for calculating distance, because if you observe the period of a Cepheid, its luminosity can be measured using Leavitt’s Luminosity vs. Period chart for Type I and II Cepheids. Once the luminosity is gotten, it can be plugged into the inverse square law to get distance. CHAPTER 18 Emission nebula is an interstellar cloud of hot, thin gasses and dust. These nebulae are located near hot luminous stars of spectral types O and B. These stars emit lots of high energy ultra violet photons which completely ionize the nearby cloud of gas. As the atoms of this nebula gas reform and cascade down to lower energy levels, they emit photons of light that make the nebula look colorful. This explains why emission nebulae are also called an H II region which stands for ionized hydrogen atoms. Dark Nebulae have a dense concentration of microscopic dust grains, which scatter and absorb light much more efficiently than single atoms. Protostars – for interstellar material to condense and form a star, the material must be relatively dense, so gravitational attraction between atoms is enhanced, and the material must be as cold as possible, so that the pressure of the medium goes down.
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Astro Study Guide - Final - CHAPTER 17 A star's parallax...

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