4/28/17 1 Galaxies and Cosmology The Discovery of Galaxies • Up to the 1920’s, astronomers were not sure exactly how far away galaxies were, and thus didn’t know how big they are! • “Spiral Nebulae” could be assumed to be inside our own Milky Way galaxy. – Planetary systems in formation? – Strangely shaped clouds? • In 1920, Shapley & Curtis debated the nature of “spiral nebulae” and the size of our Galaxy. (The debate was eventually settled using standard candles) A “Spiral Nebula” The Whirlpool Galaxy We now realize that our galaxy is only one of billions of galaxies we can see. These galaxies come in three main types: Spiral, Elliptical & Irregular Spiral Galaxies M 100 NGC 300 • Typically bright, blue in color • Look like pinwheels (sometimes with bar) A Barred Spiral Galaxy with only 2 arms.
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4/28/17
1
Galaxies and Cosmology
The Discovery of Galaxies • Up to the 1920’s, astronomers were not
sure exactly how far away galaxies were, and thus didn’t know how big they are!
• “Spiral Nebulae” could be assumed to be inside our own Milky Way galaxy. – Planetary systems in formation? – Strangely shaped clouds?
• In 1920, Shapley & Curtis debated the nature of “spiral nebulae” and the size of our Galaxy. (The debate was eventually settled using standard candles)
A “Spiral Nebula”The Whirlpool Galaxy
We now realize that our galaxy is only one of billions of galaxies we can see. These galaxies come in three main types: Spiral, Elliptical & Irregular
Spiral Galaxies
M 100 NGC 300
• Typically bright, blue in color • Look like pinwheels (sometimes with
bar)
A Barred Spiral Galaxy with only 2 arms.
4/28/17
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A Spiral Galaxy Seen Edge On
Elliptical Galaxies
Ellipticals are round, not flat like spirals, and come in a wide range of sizes
They are typically “red” in color and have less gas and dust than spirals.
The Coma Galaxy Cluster contains Ellipticals and Spirals Irregular Galaxies • Lack any distinct shape• Are generally smaller than spirals and ellipticals
Hubble Tuning Fork Spiral Galaxies (S): Classified according to spiral arms (a,b,c)
and presence of a bar (“B”) Elliptical Galaxies (E): Classified according to shape (E0-E9)