30.3 Star Groups

Constellations

• Constellations: patterns of stars and the region of space around them.

• Standard set of 88 constellations set by group of astronomers in 1930.– Acts as a road map to locate particular stars.

• Orion

• Big Dipper

• Pleiades- “seven sisters” 7 bright stars

Naming Constellations

• Modern names come from Latin.

• Names come from…– Real animals e.g. Ursa Major, “The Great

Bear” (The Big Dipper)– Imaginary animals e.g.Draco, “The Dragon”– Ancient Gods– Legendary Heroes

Multiple-Star Systems

• Binary Stars : pairs of stars that revolve around each other and are held together by gravity.

• Barycenter: center of mass. i.e. the point at which the stars revolve around.

• Estimated that more than half of all observed stars are multiple-star systems.

Star Clusters

• Clusters: groups of hundreds or thousands of stars

• Globular Clusters: Spherical shape and can contain up to 100,000 stars.

• Open Clusters: loosely shaped and rarely contains more than a few hundred stars.

Galaxies

• Galaxy: a large-scale group of stars, gas, and dust that is bound together by gravity.

• Major building blocks of universe

• Typical galaxy is 100,000 l.y. in diameter and contains 200 billion stars

• Estimated that universe contains hundreds of billion of galaxies

Types of Galaxies

• Spiral Galaxies: has a nucleus of bright stars and flattened arms that spiral around the nucleus

• Elliptical Galaxies: vary in shape from nearly spherical to very elongated. Extremely bright in the center and have no spiral arms.

• Irregular Galaxies: has no particular shapes. Have low total masses and are fairly rich in dust and gas. More rare than other galaxies.

• Elliptical Galaxies-Virgo Clusters

• Irregular

Galaxies

The Milky Way

• Spiral galaxy in which the sun is one of hundreds of billions of stars.

• All stars orbit around the center of the Milky Way Galaxy.

• Takes sun 225 million years to complete one orbit.

• Closest galaxies are 170,000 l.y. away from Earth.

• Milky Way

Galaxy

Quasars

• Discovered in 1963• Quasar: quasi-stellar radio source; a very

luminous object that produces energy at a high rate.

• Not related to star but related to galaxies.• Located in the center of galaxies and are

VERY bright• Believed that black holes are present in

those galaxies

• The arrow in this image points out the record-breaking redshift 5.0 quasar discovered by the Sloan Digital Sky Survey. That faint red dot of light represents an object that is actually a hundred times as luminous as a typical galaxy. Sky Survey astronomers identified this object as a possible high-redshift quasar on the basis of its exceptionally red color compared to ordinary stars and galaxies. Followup spectroscopy with the ARC 3.5-meter telescope confirmed that this unassuming speck was indeed the most distant quasar known to date.