Stars and Galaxies Constellations Constellations Certain groups of

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 – 100 x 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, 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*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.