Stars, Galaxies, and Constellations Stars = objects in space, made of gases, which produce their own light and heat. Earth’s nearest star is the sun (149,600,000 km away) The next nearest star is Proxima Centauri (4.24 light years away) Light year = the distance light travels in 1 year Light travels at 300,000 km/s, or about 9.5 trillion km in one year.

Measurement in Space Parallax - the apparent shift in the position of an object when viewed from two different positions

Nuclear Fusion = reactions occur when hydrogen atoms combine to form helium atoms. *this produces great amounts of light and heat* Different stars produce different amounts of energy. The amount of energy produced by a star determines the star’s color and surface temperature. Stars differ in composition, age, and size. *young stars are rich in hydrogen *older stars use up hydrogen to produce more helium

Classifying stars Based on brightness and temperature Hertzsprung-Russell Diagram

Evolution of Stars Nebula - Stars begin as a large cloud of gas and dust Main sequence – pressure from heat is in balance with gravity Giant – outer layers of the star expand and cool Supernova – star explodes White dwarf – outer layer contracts (about size of Earth) Neutron star – only neutrons can exist in the dense core Black hole – gravity is so strong that nothing can escape, not even light

Apparent magnitude – how bright the star appears from Earth. Absolute magnitude – how bright the star really is (if all stars were the same distance from Earth)

Galaxy = system of stars, dust, and gas held together by gravity. Three major classes of galaxies: Spiral Galaxy (Milky Way Galaxy) -disk-shaped with arms Elliptical Galaxy -shaped like a football Irregular Galaxy -no distinct shape

Constellations – groups of stars that form pictures in the night sky. Orion

Astronomers recognize 88 constellations. View of the north sky