Stars A star the size of our sun will burn steadily for 10 billion years, then expand to a red giant, and finally collapse into a white dwarf about the size of Earth. A star three or four times the sun’s mass will burn steadily for a shorter time, then expand into a red giant, and finally collapse, ending up as a neutron star—a super-dense star about the size of a large city. A star 50 times the sun’s mass will burn for an even shorter time and may blow up as a supernova before collapsing and eventually shrinking to infinity, becoming a black hole.

The main body in our solar system is the Sun, an average star A star is a vast collection of hydrogen gas The immense gravity in stars forces hydrogen atoms to fuse together (nuclear fusion) This nuclear fusion is the source of a star’s energy

Our Sun Our sun’s atmosphere is made of many layers Photosphere-lowest layer from which light is given off. Temperatures are about 6000K Chromosphere-Above the photosphere extending upward about 2000km. Transition zone-about 2000-10000 km above the photosphere Corona-above the transition zone and the large and the largest layer. Extends millions of kilometers into space. Temperatures in the corona are as high as 2 million K. Charged particles continually escape from the corona and move through space as solar wind.

Extra-Solar Distances The nearest star is Proxima Centauri 24 trillion miles away Stars are so far apart, we measure the distances in light years (LY) LY = The distance that light travels in 1 year 1 LY = 5,865,696,000,000 miles Proxima Centauri is 4.3 LY away

Extra-Solar Distances If we traveled 60 miles/hr to Proxima Centauri, it would take 46 million years to get there!! Voyager spacecraft travels 39,000 miles/hr Fastest spacecraft ever created Even Voyager would take 70,000 years to reach Proxima Centauri!!

Milky Way Galaxy Our Sun and Proxima Centauri are located in the Milky Way Galaxy There are about 100 billion other stars in the Milky Way Galaxy as well The diameter of the Milky Way galaxy is about 100,000 LY 590,000,000,000,000,000 miles!!! Getting a little ridiculous to measure in miles, huh?

The UNIVERSE There may be 100 billion galaxies like the Milky Way in the known universe The diameter of the known universe is estimated to be 20 BILLION LY!!! It would take a beam of light 20 billion years to travel across the universe!!