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Stars and GalaxiesPart 4: A Special Star: Our Sun1

Our Dynamic SunFrom NASAs Video Gallery2http://www.nasa.gov/multimedia/videogallery/index.html?media_id=149048022General Characteristics150 million kilometers from EarthMedium-sizedMiddle-aged (about 4.6 billion years old)YellowAlmost a perfect sphere3Layers of the Sun3 Layers of the Suns Atmosphere:Corona the outermost layergas particles can reach temperatures of 1,700,000CMillions of kilometers thickChromosphereMiddle layer Several thousand kilometers thickWhere solar flares originateAverage temperature 27,800CPhotosphereInnermost layer About 550 kilometers thickTemperatures less than 6,000COften referred to as the surface of the sun

4Heat Energy moves three ways:Conduction: from object to object by direct contactRadiation: In the form of electromagnetic waves; released and absorbed by particles in units called photonsConvection: 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.Review: How Heat Moves5Layers of the Sun3 Layers of the Suns Interior:Core The centermost portionWhere the nuclear reactions occurCan reach temperatures near 15,000,000CRadiation LayerMiddle layer Average temperature Energy travels from the core through the radiation layer as radiant energy transferred from ion to ion as photonsConvection LayerOuter layer closest to photosphereEnergy continues to move toward the surface of the sun via convection currents.

Remember: the entire Sun is made of gases/plasma (is fluid) 6

Layers of the Sun78The Active SunProminence:A type of solar storm huge bright arches or loops of gasOriginate in the chromosphereSend 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.Picture by the STEREO Project, NASAWatch Video Clip: http://en.wikipedia.org/wiki/File:Solar_prominence.ogvA solar prominence (also known as a filament) is an arc of gas that erupts from the surface of the Sun. Prominences can loop hundreds of thousands of miles into space. Prominences are held above the Sun's surface by strong magnetic fields and can last for many months. Enchanted Learning89The Active SunSolar Flares:Another type of solar stormBright bursts of light on the Suns surfaceLast under an hour but releases huge amounts of energy into space that can interfere with long-range radio communications

ASolar Flare, image taken by theTRACEsatellite (NASA).9 November 200010The Active SunSolar Wind:A continuous stream of high-energy particles released into space in all directions from the coronaSunspots:Dark, cooler areas on the suns surfaceCaused by the Suns internal magnetic field rising up to the photosphereCyclic 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.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.

11The Active SunAs the Sun consists of aplasmaand is not solid, it rotates faster at itsequatorthan at itspoles. This behavior is known as differential rotation, and is caused byconvectionin the Sun and the movement of mass, due to steeptemperature gradientsfrom the core outwards.11