what is a galaxy?

What does it consist?

Milky Way-“Galaxies kuklos”

Galileo -Numerous stars

18th century-William and Caroline Herschel

- Mapped the distances of stars

1781-Charles Messier

- Cataloged various nebulae

20th century-Harlow Shapely

- Measures the distributions and locations of globular star clusters.

1924- Edwin Hubble

-Resolved that the spiral nebulae had structures and stars- CEPHEID VARIABLES.

II. FORMATION AND EVOLUTION

Ideas about the origins and evolutions:

• collapsing dust clouds = formation of galaxies

• collisions between galaxies

Two assumptions:

1. Filled with hydrogen and helium

2. Some areas were slightly denser than others

EARLY UNIVERSE THEORIES

Two factors:

• Angular momentum (degree of spin)

• Cooling

III. DISTRIBUTION OF GALAXIES

INTERGALACTIC MEDIUM

Space between galaxies and clusters of galaxies

THE DOPPLER EFFECT

IV. GALAXY TYPES AND PARTS

Messier 32: a dwarf elliptical (E2) satellite galaxy of the Andromeda Galaxy

Messier 87: giant elliptical (E1) at the Virgo Cluster's core. It has grown very large by ``eating'' other galaxies.

NGC 2997: a large face-on spiral galaxy (Sc)

Messier 81: a large spiral galaxy (Sb).

The Triangulum Galaxy (=M 33): a small spiral galaxy (Scd) in the Local Group

NGC 1365: a barred spiral galaxy (SBbc)

NGC 3351 (=M 95): a barred spiral galaxy (SBb).

Messier 82: a starburst galaxy

V. PARTS OF A GALAXY