Stars and Galaxies

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may still be surrounded by nebula from which they formed

located in the spiral arms of a galaxy

example: Pleiades

Slide 12

More open star clusters

Slide 13

Globular Clusters

millions to hundreds of millions of stars

old! 6 to 13 billion years

mostly red giants and dwarfs

stars are clumped closely together, especially near the center of the cluster (densely)

surround our disk as a halo

Slide 14

What is a “nebula”?

A cloud in space

Made of gas and dust

Can have stars inside

Most of the ones we see are inside our Milky Way Galaxy

Different types

Slide 15

Large, massive, bright nebulae

Emission Nebula

The hot gas is emitting light

Orion image at http://hubblesite.org/newscenter/archive/releases/2006/01/image/a/results/50/

Slide 16

Colder, darker nebulae

Dark dust blocking the hot gas behind it

NOAO/AURA/NSF Image from http://hubblesite.org/newscenter/archive/releases/nebula/dark/2001/12/image/c/results/50/

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Leftovers from an Explosion

Supernova remnant

(smaller, less gas)

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What is a “galaxy”?

A large group of stars outside of our own Milky Way

Made of billions to trillions of stars

Also may have gas and dust

Spiral, or elliptical, or irregular shaped

Slide 19

Spiral galaxy--Andromeda

NOAO/AURA/NSF

Slide 20

Elliptical Galaxies

Images at

Slide 21

Irregular Galaxies

NASA and NOAO/AURA/NSF Images at http://hubblesite.org/newscenter/archive/releases/galaxy/irregular/2005/09/results/50/ , http://www.noao.edu/image_gallery/html/im0560.html , and http://www.noao.edu/image_gallery/html/im0993.html

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Our Galaxy: the Milky Way

has about 200 billion stars, and lots of gas and dust

is a barred-spiral (we think)

about 100,000 light-years wide

our Sun is halfway to the edge, revolving at half a million miles per hour around the center of the Galaxy