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

• There are trillions of stars in the universe.

• Most stars seen from Earth are within 100 light-years from Earth

Star Groups

• 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

Constellations

• 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

Dividing up the Sky

• Many names come from Latin

• Real animals Ursa Major (Great Bear) or imaginary animals Draco(Dragon)

• Ancient or Legendary heroes (Orion’s belt)

Naming Constellations

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

• 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

Multiple-Star System

• Nebulas collapse to form groups of 100’s to 1,000’s of stars called clusters

• There are Global clusters and Open clusters

Star Clusters

• 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

Galaxies

• Scientists look at certain stars absolute and apparent magnitude to determine distance to the galaxy

• Galaxies are classified by shape

1. Spiral galaxies

2. Elliptical galaxies

3. Irregular galaxies

Distance to 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

1) Spiral Galaxies

• They vary in shape from spherical to elongated

• They are extremely bright in the center and do not have spiral arms

2) Elliptical Galaxies

• They have no particular shape

• Have low total masses and rich in dust and gas

• Rarest type of galaxy

3) Irregular Galaxies

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

• 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

The Milky Way

• 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

Quasars

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