Notes 30.3 Star Groups Std 2a: Know that the solar system is located in the outer edge of the disc-shaped Milky Way galaxy Std 2b: Know galaxies are made of billions of stars and comprise most of the visible mass of the universe Objective 1: Describe the characteristics that identify a constellation Objective 2: Describe the three main types of galaxies Objective 3: Explain how a quasar differs from a typical galaxy

Star Groups There are trillions of stars in the universe. Most stars seen from Earth are within 100 light-years from Earth

Constellations Star groups that form patterns can be identified by using a star chart The sky has been divided into 88 regions Describes the locations of celestial objects Constellation - a group of stars organized in a recognizable pattern

Dividing up the Sky The constellations are used to locate particular stars The stars in a constellation appear close together when viewed from Earth, but they are very far from each other

Naming Constellations Many names come from Latin Real animals Ursa Major (Great Bear) or imaginary animals Draco(Dragon) Ancient or Legendary heroes (Orion’s belt)

Objective 1: Describe the characteristics that identify a constellation How many regional division of the sky exist? 88 Divisions What is group of stars organized into patterns? Constellation What language was used to name many constellations? Latin What are 2 other ways constellations are named? Animals or legends/heroes

Multiple-Star System When two or more stars are closely associated, they form multiple-star systems Binary Stars - pairs of stars that revolve around each other and held together by gravity Multiple-star systems sometimes have more than two stars Astronomers estimate that more than half of all observed stars are part of a multiple star system

Star Clusters Nebulas collapse to form groups of 100’s to 1,000’s of stars called clusters There are Global clusters and Open clusters

Galaxies A large-scale group of stars, gas, and dust that is bound together by gravity is called a galaxy The Milky Way Galaxy (which we live), has a diameter of about 100,000 light years and more than 200 billion stars There are hundreds to billions of galaxies

Distance to Galaxies Scientists look at certain stars absolute and apparent magnitude to determine distance to the galaxy Galaxies are classified by shape Spiral galaxies Elliptical galaxies Irregular galaxies

1) Spiral Galaxies They have a nucleus of bright stars and flattened arms that spiral around the nucleus Some have a straight bar of stars that run through the center these are called barred spiral galaxies

2) Elliptical Galaxies They vary in shape from spherical to elongated They are extremely bright in the center and do not have spiral arms

3) Irregular Galaxies They have no particular shape Have low total masses and rich in dust and gas Rarest type of galaxy

Objective 2: Describe the three main types of galaxies What is a large-scale group of stars, gas, and dust that is bound together by gravity? galaxy What are the 3 types of galaxies? Spiral, elliptical and irregular Which galaxy is very bright and does not have arms? Elliptical Which galaxy is the rarest type? Irregular

The Milky Way A Spiral Galaxy in which the sun is one of hundreds of billions of stars the name comes from the cloudlike “milky” appearance it takes the sun about 225 million years to orbit around the galaxy

Quasars Quasar is a shortened term for quasi-stellar (“similar to star”) radio source Bright, old and most distant objects in the universe They are related to galaxies not stars They are at the center of young galaxies, causing their centers to be very bright Associated with giant black holes in the center

Objective 3: Explain how a quasar differs from a typical galaxy What is a quasar? Quasi-stellar radio source Where are quasars found? Young galaxies What are they related to? Galaxies not stars! What is commonly associated with a quasar? giant black hole