AST201H1 Lecture 11: AST 201 - lecture 11
16 Feb 2019
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Document Summary
In the previous lecture we discussed how to find certain properties of stars without having to go send probes to the stars. We can find the chemical composition by observing spectral lines. We can find the distance of stars by measuring the parallax. We find the luminosity by calculating the distance and brightness. Plot surface temperature on the x-axis and the luminosity on the y-axis. Example: a certain absorption line on the spectrum of blue light is produced when an electron in a hydrogen atom jumps from level 2 to level 4. In a cool star, electrons are sitting in low energy levels from which they can"t absorb this wavelength, so the line is weak. In very hot stars, the gas is ionized so there are very few electrons in the correct energy level, so the line is weak. Blue stars are very, very hot, and on the opposite side of the spectrum are cooler stars.
