26.+Stars,+Galaxies,+and+the+Universe



The Whirlpool Galaxy, also known as M51, is a spiral galaxy about 23 million light-years from Earth. Its interactions with the yellowish dwarf galaxy NGC 5195 are of interest to astronomers because the galaxies are near enough to Earth to be well-studied.

Decades ago astronomers could not tell if these two galaxies were just passing each other but radio astronomy has supplied astronomers with important data outlining their interactions. Using this data, astronomers have simulated the interaction. NGC 5195 came from behind and then passed through the main disk of M51 about 500 to 600 million years ago. The dwarf galaxy crossed the disk again between 50 and 100 million years ago and is now slightly behind M51. These interactions appear to have intensified the spiral arms that are the dominant characteristic of the Whirlpool Galaxy.

Astronomers are able to learn about objects unimaginably far away from Earth using telescopes that sense all wavelengths on the electromagnetic spectrum. Imagine what Galileo would do if he could see the images and data astronomers have available to them now.

Lessons
26.1 Stars 26.2 Galaxies 26.3 The Universe

**Khan Academy**

 * 1) [|Scale of Earth and Sun]
 * 2) [|Scale of Solar System]
 * 3) [|Scale of Distance to Closest Stars]
 * 4) [|Scale of the Galaxy]
 * 5) [|Intergalactic Scale]
 * 6) [|Hubble Image of Galaxies]
 * 7) [|Big Bang Introduction]
 * 8) [|Radius of Observable Universe]
 * 9) [|(Correction) Radius of Observable Universe]
 * 10) [|Red Shift]
 * 11) [|Cosmic Background Radiation]
 * 12) [|Cosmic Background Radiation 2]
 * 13) [|Cosmological Time Scale 1]
 * 14) [|Cosmological Time Scale 2]
 * 15) [|Four Fundamental Forces]
 * 16) [|Birth of Stars]
 * 17) [|Becoming a Red Giant]
 * 18) [|White and Black Dwarfs]
 * 19) [|A Universe Smaller than the Observable]
 * 20) [|Star Field and Nebula Images]
 * 21) [|Parallax in Observing Stars]
 * 22) [|Stellar Distance Using Parallax]
 * 23) [|Stellar Parallax Clarification]
 * 24) [|Parsec Definition]
 * 25) [|Hubble's Law]
 * 26) [|Lifecycle of Massive Stars]
 * 27) [|Supernova (Supernovae)]
 * 28) [|Supernova clarification]
 * 29) [|Black Holes]
 * 30) [|Cepheid Variables 1]
 * 31) [|Why Cepheids Pulsate]
 * 32) [|Why Gravity Gets So Strong Near Dense Objects]
 * 33) [|Supermassive Black Holes]
 * 34) [|Quasars]
 * 35) [|Quasar Correction]
 * 36) [|Galactic Collisions]
 * 37) [|Earth Formation]