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.
Nebulae: a cloud of dust and gas that we see in light
Emission Nebulae or Bright Nebulae: a glowing gas (hydrogen); e.g. Great Nebula in Orion, heated by the Trapezium
Absorption Nebulae or Dark Nebulae: dark dust clouds; e.g. Horsehead Nebula
Reflecting Nebulae: reflecting dust cloud; e.g. Pleiades in Taurus
Planetary Nebulae: excited by central star; e.g. Dumbbell Nebula
Stars form in Giant Molecular Clouds about 100,000 to 1 million solar masses. A few thousand in the Milky Way Galaxy, Giant Molecular Clouds break into denser bits, contract, and eventually form stars. The Orion Molecular Cloud has about 500 stars. The Trapezium and the Orion Nebula have solar masses of matter with young stars.
Non-stellar galactic objects reside in HII regions with molecular clouds of pre-main sequence stars and dense clumps of dust.
Protostars and newborn stars about 1/2 to 1 solar mass reside in Molecular Clouds.