NATS 1745 Lecture Notes - Lecture 20: Spiral Galaxy, Inverse-Square Law, Cosmic Distance Ladder
2 Apr 2016
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Document Summary
Shapley as big as our galaxy all of the spiral nebulae" lie inside our galaxy. Curtis spiral nebulae were distant separate entities, like our own galaxy. He discovered a cepheid in the andromeda spiral nebula, and calculated the distance at a few million light years much larger than anyone had anticipated they were island universes". Looking at stars at the edge of the galaxy. Astronomers measured the doppler shifts to calculate the rotation speeds of the stars. Calculated what the speed should be" based on the observed mass of the galaxy using newton"s laws. Expected: far from the center of the galaxy speeds should be a lot lower than observed. To get large speeds the stars need to feel the pull of gravity from some kind of unseen material: dark matter. A type of object that has a constant absolute brightness. Allows astronomers to get its distance vie the inverse square law.
