PCS 181 Lecture Notes - Lecture 3: Observable Universe, Photon, H I Region
8 Nov 2016
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Document Summary
Dust and gas that occupy space between stars. Stars form in the dust/gas clouds in space. Dust: is ~1% of total visible mass in space is a mixture of: elongated, tiny grains of dirty ice, grains of graphite (carbon, silicate particles (silicons, complex molecules. Light from a star passes through the dust. The dust particles are ~same length as blue wavelength s. The dust scatters blue wavelengths more than red wavelengths. More red photons pass unhindered through the dust and reach observer. There exists ~100 times more gas mass than dust mass in the universe. These are clouds of neutral (not ionized) hydrogen, ionized = take electrons away. The cold hydrogen gas is in its ground state (n=1 orbit) Hydrogen atom has 2 possible ground state configurations. State (parallel) to the opposed state (antiparallel) cold neutral hydrogen clouds in space emit a wavelength.
