Notes for HCDE Workshop on Sun and Seasons Feb. 4, 2009 The Sun Is a star Made of gases Is our primary source of energy A star in the Milky Way galaxy Galaxy- group of billions of stars. 70% hydrogen and 28% helium Light (radiation) The Nine Planets website has all of this excellent information: http://seds.lpl.arizona.edu/nineplanets/nineplanets/sol.html The Sun contains 99.8% of all of the mass in our Solar System. It is a yellow, medium-temperature star– 9,981°F (5527°C) on the outside and 28 million°F (15 million°C) in the center. Image at http://science.nasa.gov/headlines/y2007/images/chromosphere/LimbFlareJan12_strip2.jpg Lunar and Planetary Institute

Notes for HCDE Workshop on Sun and Seasons Feb. 4, 2009 How Big is the Sun? About 110 times wider than Earth Or 1.3 million times bigger than Earth Only part of the sun that can’t be seen is the atmosphere. Our Sun is 865 thousand miles (1,390,000 km) wide. Even a medium-sized sunspot is as big at the Earth! Photo from http://sohowww.nascom.nasa.gov/bestofsoho/ Atmosphere- layer of gases that surrounds the earth. Photo from http://sohowww.nascom.nasa.gov/bestofsoho/bestofsoho.html Lunar and Planetary Institute

How does our Sun compare to other Stars? Notes for HCDE Workshop on Sun and Seasons Feb. 4, 2009 How does our Sun compare to other Stars? Active stars range in size from supergiants to dwarfs Stars range from very bright (supergiants) to very dim (dwarfs) Stars range from very hot blue on the outside (O class) to cool red on the outside (M class) Our Sun is a dwarf—medium mass Our Sun is a medium-bright dwarf Our Sun is in-between--yellow Supergiants can be hundreds to thousands of times bigger than our Sun, and possibly up to 100 times more massive than our Sun. The smallest stars are about 1/100 of the Sun’s mass. Temperature ranges for the outside of a star (spectral classification): O (blue), B (blue-white), A (white), F (white-yellow), G (yellow), K (orange), M (red) Very large stars can be very hot on the outside (O class) or cool on the outside (all the way down to M class)—all large stars are extremely hot in their cores. All small active stars (excludes remaining cores of old stars) are cooler on the outside and in their cores, compared to the most massive stars. Lunar and Planetary Institute

So is our Sun an average star? Notes for HCDE Workshop on Sun and Seasons Feb. 4, 2009 So is our Sun an average star? No—most stars are smaller and cooler than our Sun BUT Most of the bright stars we see are bigger and hotter For more details and a graph, go to Nick Strobel’s Astronomy Notes: http://www.astronomynotes.com/starprop/s14.htm Lunar and Planetary Institute

Notes for HCDE Workshop on Sun and Seasons Feb. 4, 2009 More on Sunspots Our Sun has an activity cycle of 11 years Sunspots- dark areas on the sun’s surface. Basic information and image at http://starchild.gsfc.nasa.gov/docs/StarChild/questions/question17.html Sunspot cycle and detailed data for activities at http://solarscience.msfc.nasa.gov/SunspotCycle.shtml Images at http://starchild.gsfc.nasa.gov/docs/StarChild/questions/question17.html and http://solarscience.msfc.nasa.gov/SunspotCycle.shtml Lunar and Planetary Institute

Sun as a Source of Energy Notes for HCDE Workshop on Sun and Seasons Feb. 4, 2009 Sun as a Source of Energy Plants need light for photosynthesis Without its heat, the only inhabitable areas on Earth would be near volcanic vents Images from http://nasadaacs.eos.nasa.gov/articles/2005/2005_rainforest.html and http://planetquest.jpl.nasa.gov/TPF/tpf_book/gallery/4-2a.html Lunar and Planetary Institute