3What is a galaxy?Stars are not uniformly distributed through the universe but are unevenly clustered into groups.
4What is a galaxy?A galaxy is a massive system of stars, dust, and gas held together by gravity.Galaxies contain billions of stars.
5What is a galaxy?Within galaxies, are smaller groups of stars known as star clusters.A “cluster” is a group of stars inside the galaxy.M13 Clusterin our galaxycan see with binocularsover 100,000 stars
6What is a galaxy? Hubble identified three types: Spiral Elliptical Irregular
7Spiral GalaxyShaped like a flattened disk with a bulging center and “arms” that curve in a spiral patternRich with dust and gasesNew stars are in “arms”Old stars are in the center(e.g.) Milky Way
8Elliptical GalaxyShaped like a sphere or “egg” because stars are close together near the center & farther apart on the outside edgesVery little dust and gasVery few new starsMostly old stars
9Irregular Galaxy No definite shape or organization Contains clouds of dust and gasesContains a mix of old and new stars
10Milky WayOur solar system is located in a spiral galaxy called the Milky Way Galaxy.
11Milky Way 3 1 2 1 – Closest Milky Way “arm” 2 companion galaxies: 2 - Large Magellanic Cloud3 - Small Magellanic Cloud
12Distances between Galaxies Galaxies are so far away that even the closest galaxies appear as fuzzy patches of light.
13Distances between Galaxies Galaxies are grouped together into clusters, which form superclusters.The Milky Way is part of a cluster called the Local Group.The farthest galaxies from Earth are about 14 billion light years away.
15Big Bang TheoryIn the late 1920s, Hubble discovered that most of the galaxies he observed were moving away from Earth.This could only be explained if the entire universe was expanding.
16Big Bang TheoryThe Big Bang Theory states the expansion of the universe began about 14 billion years ago.The universe was a tiny point that contained all the energy and matter of the universe.The universe began to expand rapidly, and cool.
17Big Bang TheoryThe universe was too hot to form elements for several hundred thousand years.The universe consisted of radiation and subatomic particles.As the universe cooled, hydrogen and helium atoms formed.
18Big Bang TheoryGalaxies began forming several hundred million years after the Big Bang.Clouds of hydrogen and helium possibly became more dense in some regions.
19Big Bang TheoryThe dense regions began to clump and form stars.
20Dark Matter & Dark Energy Scientists can calculate how much mass the universe should contain by the way galaxies move through space.All the matter they can detect added together is less than the amount needed.The missing matter is called dark matter.The missing energy needed to explain the expansion of the universe is called dark energy.
21Which is the shape of the Milky Way? A flat B elliptical C irregular 12.3 GalaxiesWhich is the shape of the Milky Way?A flatB ellipticalC irregularD spiral
22How old is the universe thought to be? 12.3 GalaxiesHow old is the universe thought to be?A several hundred thousand yearsB 1 million yearsC 14 billion yearsD 63,000 million years
23A cluster is a group of ____. A stars B solar systems C galaxies D planets
24The average distance between Earth and the Sun is called a(n) ____. SCI 4.cThe average distance between Earth and the Sun is called a(n) ____.A light-yearB astronomical unitC angstromD solar unit
25SCI 2.gWhat causes clouds of gas and dust to form clumps in interstellar space?A solar windsB gravityC electronsD dark matter
26Galaxies have what three shapes? A cluster, group, and spiral SCI 4.aGalaxies have what three shapes?A cluster, group, and spiralB supercluster, cluster, and groupC spiral, elliptical, and irregularD regular, irregular, and flat
27Vocab – Galaxies text p. 528-534 galaxyspiral galaxyMilky Wayelliptical galaxyirregular galaxyrandomlybig bang theoryHIGHLIGHT!!!