Types of Galaxies

What is a galaxy? A giant cluster of stars, gases,and dust held together by gravity. Contains hundreds of billions of stars Three shape classifications: Spiral Elliptical Irregular

Spiral Galaxy Shaped like a flattened disk with a bulging center and “arms” that curve in a spiral pattern Rich with dust and gases Form new stars (mostly in dense material of “arms”) Center bulge is made up of old stars

Milky Way The name of the galaxy where our solar system is located. It is a “barred” spiral with a dense “bar” of stars at the center from which the arms branch out. This is a drawing, not a real picture as we do not have probes outside our galaxy to take the pictures.

Elliptical Galaxy Shaped like a sphere or “egg” Most stars are old stars Very little gas and dust Stars are close together near center Stars on outside edge are farther apart

Irregular Galaxy No definite shape or organization Contain a mix of old stars, new stars, clouds of dust and gases

The Local Group

The Big Bang Theory The most popular theory explaining the beginning of our Universe and everything in it. The idea that the universe began as a tiny, very hot point or “singularity” and began to expand rapidly, then cool. Still continuing to expand (like a tiny balloon that expands, but never pops).

Homework You will write a “Step-Up-To-Writing” style summary paragraph. The topic sentence is : “Galaxies can be classified as spiral, elliptical or irregular.” Your paragraph should be at least 8 sentences. Topic sentence should be followed by a yellow detail sentence then a red example sentence (repeat until you have at least 3 yellow sentences and a red for each). End with a green conclusion sentence.