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 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.