What does the “M” in M31 or M11 stand for? Messier[Me-Si-Eh]
Charles Messier (1758-1772), a French astronomer, identified about 110 diffuse fuzzy objects that he named “Messier objects.” Messier then cataloged these objects in his Messier Catalog. He also discovered 13 comets; finding comets was a way to make a name astronomers of the 18th century).
M42: Orion Nebula
local region in the Milky Way (~1,300 light years away) with new stars
appears mostly red due to hydrogen gas abundance
~12 million light years away
clouds of glowing hydrogen blown out, released by recent star formation
M31: Andromeda Galaxy
hundreds of nebulae (discovered 20th century)
with George E. Hale’s idea and Hooker’s money –> the Hooker Telescope (100-inch in diameter, 11 years to build, $100 million)
Today, the Sloan Digital Sky Map holds 15 Terabytes of data on the Universe.
In the Southern Hemisphere, the Magellanic Clouds, or the galaxy’s satellite galaxies (revolves around Milky Way), are visible. The Magellanic Clouds are named for the Portuguese explorer Ferdinand Magellan, the first circumnavigator of the world. Because of interstellar dust (rocky planets and other material), we can only see 6,000 stars, but the Milky Way has 100 billion stars total. The farthest are 4,000 light years away. Earth’s atmosphere smears the sky, so stars appear to twinkle. About 10^6 stars— old as the universe— inhabit In globular clusters (~200 in Milky Way’s halo).
All pictures of the Milky Way are artists’ conceptions because no telescope can travel high enough (billions of light years) to capture the entire galaxy.
Milky Way – Structure
Shapley’s Subdivision of the Milky Way
Nuclear Bulge: (10^6 solar masses) nucleus in the center, old stars (red)
The Disk: (10^11 solar masses) thin, diffuse layer of material revolving around the bulge; the Sun is half-way on the disk; all young stars
The Halo: hot gas about 100,000 K
Galactic Corona: mass exists but unseen; 5-10 times as much mass as the nucleus, disk, and halo together, 95% of galaxy mass unknown matter
Visible Matter: 96% stars, 4% interstellar gas
(13.6 billion years ago) A gas cloud of 75% hydrogen and 25% helium with mass ~ 1 trillion solar masses
Contraction and rotation form spherical shape
Inner part flattens to form disk of younger stars
Galactic rotation forms spiral arms
Supernovae gives off more heavy elements that eventually become the Sun