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Lecture

Astro week 9 lecture 1.docx

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Department
Astronomy
Course
AS101
Professor
Patrick Mc Graw
Semester
Winter

Description
AS101 Week 9 Lecture 1 Spectra: Quick Summary  Continuous (a.k.a. thermal, a.k.a blackbody) spectrum: produced by a hot, dense object.  Hotter objects produce more light overall, and also more short wavelengths compared to cooler ones.  Line spectra (emission or absorption): produced by low-density gases absorbing or emitting light at specific frequencies only. Line spectra show “chemical fingerprints” for the particular atoms in the gas.  Ex of continuous spectrum: filament in incandescent light bulb, heating element on toaster, surface of a star Three Basic Type of Spectra  Continuous (thermal)  Emission (line)  Absorption (line) The Doppler Effect  When we observe spectral lines from an astronomical source, (for example, all the spectral lines of hydrogen), we can compare them with a reference spectrum from hydrogen gas in the lab.  If the source is moving toward us, the spectral lines will be shifted to higher frequencies (blueshift) compared to the reference spectrum.  If the source is moving away from us, the lines will be shifted to lower frequencies (redshift).  Note: the doppler effect can only tell us about radial velocities (i.e., motion toward or away from the observer)  It cannot give us any information about the transverse (sideways motion)  Farther away the galaxy, the quicker its moving away What are the main objects in the solar system?  The Sun o The sun includes most of the matter in the solar system o Mostly hydrogen and helium. o Biggest object, contains most mass  The Planets o Terrestrial planets (Mercury, Venus, Earth, Mars) are small, rocky, and closer to the Sun. o Jovian planets (Jupiter, Saturn, Uranus, Neptune) are large, gassy (contain a lot more hydrogen, helium, methane, etc.) and farther from the Sun. o Jovian planets also have more moons than the terrestrial planets. o Jovian planets all have rings, but Saturn's are the most noticeable. o Order of planets by distance from the Sun: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune. o “My Very Excellent Mother Just Served Us Nachos.”  Meteoroids, Asteroids, Comets and Dwarf Planets Other Parts of the Solar System: the Asteroid Belt  Asteroid belt is a region at distances approximately 2-4 au from the Sun, between the orbits of Mars and Jupiter. 21  Total mass adds up to about 3x10 kg, or 4% of the Moon's mass.  Includes between 700,000-1,700,000 objects with diameters of 1km or more.  Rocky and metallic, like terrestrial planets, but some also contain water ice.  Actually extremely spread out, not crowded together as in a lot of SF movies. (Several spacecraft have passed through it without hitting anything.) Still, they collide with
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