AST201H1 Chapter Notes - Chapter 22: Elliptical Galaxy, Spiral Galaxy, Cosmic Dust

• School: UTSG
• Department: Astronomy & Astrophysics
• Course: AST201H1
• Professor: Michael Reid

Document Summary

Dark matter and dark energy have never been directly observed, but each has been proposed to exist because it seems the simplest way to explain a set of observed motions in the universe. Dark matter is the name given to the unseen mass whose gravity governs the observed motions of stars and gas clouds. Dark energy the name given to whatever may be causing the expansion of the universe to accelerate. Interstellar dust obscures our view of disk stars more than a few thousand light-years away from us, making it very difficult to measure stellar velocities. A diagram called a rotation curve, which plots the rotational velocity of stars or gas clouds against their distance from the center of galaxy, summarizes the results of these orbital velocity measurements. Solar system the rotation curve for our solar system drops off with distance from the.