Stars and Galaxies

1. Stars and Galaxies Part 4: A Special Star: Our Sun

2. Our Dynamic SunFrom NASA’s Video Gallery

3. General Characteristics • 150 million kilometers from Earth • Medium-sized • Middle-aged (about 4.6 billion years old) • Yellow • Almost a perfect sphere

4. Layers of the Sun 3 Layers of the Sun’s Atmosphere: • Corona – • the outermost layer • gas particles can reach temperatures of 1,700,000°C • Millions of kilometers thick • Chromosphere • Middle layer • Several thousand kilometers thick • Where solar flares originate • Average temperature 27,800°C • Photosphere • Innermost layer • About 550 kilometers thick • Temperatures less than 6,000°C • Often referred to as the surface of the sun

5. Review: How Heat Moves Heat Energy moves three ways: • Conduction: from object to object by direct contact • Radiation: In the form of electromagnetic waves; released and absorbed by particles in units called photons • Convection: The movement of heat through the flow of a liquid or gas (fluids); Hotter fluids are less dense and therefore rise above cooler fluids, while cooler fluids are more dense and therefore sink.

6. Layers of the Sun 3 Layers of the Sun’s Interior: • Core – • The centermost portion • Where the nuclear reactions occur • Can reach temperatures near 15,000,000°C • Radiation Layer • Middle layer • Average temperature • Energy travels from the core through the radiation layer as radiant energy transferred from ion to ion as photons • Convection Layer • Outer layer closest to photosphere • Energy continues to move toward the surface of the sun via convection currents. Remember: the entire Sun is made of gases/plasma (is fluid)

7. Layers of the Sun

8. The Active Sun Prominence: • A type of solar storm • huge bright arches or loops of gas • Originate in the chromosphere • Send gases and energy into space On September 29, 2008 this magnificent eruptive solar prominence lifted away from the Sun's surface, unfurling into space over the course of several hours.  Watch Video Clip: http://en.wikipedia.org/wiki/File:Solar_prominence.ogv Picture by the STEREO Project, NASA

9. The Active Sun Solar Flares: • Another type of solar storm • Bright bursts of light on the Sun’s surface • Last under an hour but releases huge amounts of energy into space that can interfere with long-range radio communications A Solar Flare, image taken by the TRACE satellite (NASA). 9 November 2000

10. The Active Sun Solar Wind: • A continuous stream of high-energy particles released into space in all directions from the corona Sunspots: • Dark, cooler areas on the sun’s surface • Caused by the Sun’s internal magnetic field rising up to the photosphere • Cyclic increase in sunspot activity every 10-11 years Ocular projection of the sun with large sunspots using a spotting scope (50mm diameter, 45x magnification) and a sheet of paper approx. 30 cm from the ocular. 

11. The Active Sun Rotation of the Sun: • Movement of sunspots across the surface indicates that the sun rotates on its axis • The middle of the sun appears to rotate once every 25 days. • Closer to the poles a complete rotation takes over 33 days. This is possible because the Sun is plasma, not solid like the Earth. Remember: Plasma is a fourth state of matter, ionized gas, found primarily in stars.