Galaxies and Stars Galaxies – billions of star groups more than 100 billion galaxies, each containing billions of stars. Galaxies have different shapes: Spiral Galaxies – pinwheel-shaped: spiral arms that rotate nucleus in the center 30% of all galaxies, including the Milky Way (our galaxy) The oldest stars are located near the nucleus. Elliptical Galaxies: spherical or oval shape: contain little dust and gas 60% of all galaxies very old stars and very little nebulae (a cloud of gas and/or dust in space) Irregular Galaxies: no orderly shape and are very rare. 10% of all galaxies Galaxies and Stars

Big Bang Theory At one time, the universe was a dense, hot, supermassive ball. About 13.7 billion years ago, a violent explosion occurred sending material in all directions into space. This marked the beginning of the universe. Eventually, matter cooled and condensed into galaxies, stars, and planets.

Support for the Big Bang Theory Red shifts Cosmic background radiation Radio signals coming from every direction in space. Believed to be created by the big bang explosion.

The Expanding Universe 1929 – Edwin Hubble found that the universe is expanding Estimated distances, relative brightness, Doppler red shifts Dimmer galaxies had greater red shifts  farthest from Earth Hubble’s Law: the more distant the galaxies have greater red shifts, therefore they are moving away at faster speeds.

The End of the Universe Some scientists believe the universe will continue to expand. The stars will slowly burn out creating invisible matter and black holes that continue to travel outward. Other scientists believe the universe will end in the “big crunch.” Gravity will pull galaxies together. Galaxies will collide, creating a high-energy, high-density mass – the opposite of the big bang.

Evidence for the End of the Universe The evidence leads to the belief of an ever-expanding universe. The average density must be greater than the critical density (1 atom for 1 m3) in order for gravity to stop the outward movement of matter and pull it inward. Current predictions have the average density to be less than the critical density. Studies show the universe is expanding faster now than in the past. There may be uncertainties (such as undetected matter) that scientists do not know about that may provide evidence that the big crunch can actually happen.

Solar System Until recently, there have been 9 planets in our solar system. Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto In 2003, scientists discovered more planets orbiting in our solar system.

The Sun

Terrestrial Planets Mercury Venus Earth Mars

Jovian Planets Jupiter Uranus Saturn Neptune

The New “Dwarf” Planets Sedna (2003 UB 313) Charon Pluto Ceres Asteroid

Assignment Solar System Assignment