3.3 Astro 1 Section 1 Professor Brandt

3.3 Astro 1 Section 1 Professor Brandt - Astro 1 Section 1...

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Astro 1 Section 1 Professor Brandt Wednesday March 3rd 1999 Announcements: Lecture notes: Class 23 " Dark Matter " - many/most astronomers think that greater than 90% of the Universe exists in a "dark" form that we cannot see at any wavelength. Today I will explain why we think this. First of all what if the sun emitted no light. Would we know it is still there? yes how? gravitational influence. Astronomers use this same trick over and over - detect the evidence of something we can't see by its gravitational influence on things we can see. - giant black hole in center of our Galaxy - black holes in binary star systems. Dark Matter in the Milky Way. First lets do a rough calculation to estimate the amount of mass interior to orbit of sun. Remember that sun orbits in disk of Galaxy. In first section of class we learned about Kepler's Laws in particular the 3rd law. Ma + Mb = a 3 /p 2 Ma Mb in solar masses a in AU p in years. This also works roughly to figure out amount of mass interior to Suns orbit around center of Galaxy.
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