Stars and Galaxies

Constellations Constellations- Certain groups of stars named after animals, characters in mythology, or familiar objects From earth constellations look like groups of stars close together Brightest star in the winter sky is Sirius 88 constellations Star Polaris – North Star

Appear to move because earth is moving Stars also appear to change position in the sky throughout the year Earth revolves around the sun As earth orbits different constellations come into view while other disappear Appendix j pg 674-675

Absolute and Apparent Magnitudes Absolute Magnitude Is a measure of the amount of light is actually given off Apparent Magnitude Amount of light received on earth Example: Sirius – 100x closer to earth then Rigel, therefore appears brighter

Determining distances Parallax Apparent shift in the position of an object when viewed from two different positions The nearer an object is to the observer, the greater its parallax Distance in space are measures in light years Light year is the distance light travels in 1 year Light travels at 300,000 km/s

Nearest star other then the sun is Proxima Centuri 4.2 light years away It takes 4.2 years for light from that star to reach you Stars temperature is determined by the color of the star

Very hot stars – blue white color Cool stars – orange or red Stars temperature close to the sun – yellow

Evolution of Stars H-R Diagram Graph that shows relationship a stars temperature to its absolute magnitude Most stars fit into the main sequence of stars Hot blue bright stars (upper left) Cool Red dim stars (lower right) Sun is a yellow medium temp. star 90% of all stars are Main Sequence

The other 10% are Super Giants, Giants, White Dwarfs Evolution of Stars Stars begin as a large cloud of gas and dust called a nebula At high temperature Fusion begins Main sequence star forms Begins to use its hydrogen

When hydrogen fuel runs out, expands and becomes a giant Core collapses Outer portion of the giant blows away forming a white dwarf Eventually the white dwarf uses its fuel and becomes a cold dead star If a super giant (30 times our sun) collapses it may turn into a black hole

Black Hole

The Sun

The Sun 99% of all matter in our solar system is the sun It is the center Makes life possible on earth Just an average star Enormous ball of gas, fusing hydrogen into helium at its core

Layers of the suns atmosphere Photosphere – lowest layer from which light is given off Temp. 6000* C Chromosphere- Upward about 6000 Km Corona Largest layer, extend out millions of km in space Temp. 2, 000,000*C Charge particle escape causing solar wind

Sunspots Dark areas on the suns surface, which are cooler then their surroundings Sun rotates Rotates faster at its equator than at its poles It takes 25 days for a sunspot to go around the sun at the equator

Prominences and flares Intense magnetic field associated with sunspots may cause prominence, huge arching columns of gases So eruptive that material from the sun is blasted into space 1000 Km/sec

Sun is a main sequence star Most star are in a system in which two stars orbit each other (Binary system) Our sun does not do this Some stars move through space as star cluster

Galaxies

Galaxies Large group of stars, gas, and dust held together by gravity Galaxies are separated by huge distances, often millions of light years Three types of galaxies Elliptical Spiral Irregular

Types of Galaxies

Elliptical is the most common Vary in size Football shaped Cluster of galaxies that the Milky Galaxy belongs to is called Local Groups Spiral Galaxies have spiral arms Milky Way is a spiral Galaxy

Irregular Galaxies Many different shapes Cloud of Magellan Orbit

Spiral

Irregular

Elliptical

Milky Way Galaxy In our galaxy, all stars orbit a central region 200 million years for the sun to orbit this central region Contains more then 200 billion stars

                                                       

Expansion of the Universe When a Spectrograph is used to study light from galaxies beyond the Local group, there is a red shift in the light Because there is a red shift in the light, all galaxies must be moving away from earth Doppler Shift Big Bang Theory states that between 15 and 20 billion years ago, the universe began expanding out of an enormous explosion

There is evidence that supports the Big Bang Theory Scientist have discovered radiation in space that they believe was created by the explosion All matter exerts a gravitational force If there is enough matter, gravity will halt expansion A big crunch would result

Meteors A meteoroid is matter revolving around the sun or any object in interplanetary space that is too small to be called an asteroid or a comet A meteorite is a meteoroid that reaches the surface of the Earth without being completely vaporized term meteor describe the streak of light produced as matter in the solar system falls into Earth's atmosphere creating temporary incandescence resulting from atmospheric friction.