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Measurable Properties of our Sun
• Nearest star• Distance ~ 1 AU• Radius ~ 7 x 108 m– 100x earth radius– from distance, angularsize• Mass ~ 2 x 1030 kg– 333, 000x Earth mass– from orbits of planets• Temperature ~ 5800 K– from peak of intensity atwavelength of 500 nm
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Composition of our Sun
- • Sun is gaseous-violent, bubbling up close-too hot to be solid, liquid•
- Chemical composition- 71% Hydrogen- 27% Helium- 2% other elements(at
- surface)
- • Sun’s layers- more dense inside- less dense near surface
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Outside of the Sun
Photosphere – visible surface- sunspots Chromosphere – layer just abovephotosphere- magnetic activityspicules Corona – extended, rarified surface
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Outside the surface of the SUN
- 1. Photosphere - SunspotsGranulation
- 2. Chromosphere - spicules
- 3. Corona- Coronal holes- Prominences - Solar flares
- 4. Solar Wind
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PHOTOSPHERE:
- visible surface of the SunTwo features:• sharp edge“limb”• brighter
- incenter thanalong the limb“limb darkening”limb less denseless light
- emitted
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Photosphereappears smooth, butis actually granular• Granules ~ 1000 kmacross• Convection cells ofgas rising and falling
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Photosphere: Sunspots
Sunspot – magnetic features on photosphere- cooler than photosphere (DARK) ~ 3-4000 K- many 10,000 km’s across!
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Sunspot Cycle:•
The number of sunspots changes daily• The location of Sunspots changes daily
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Sunspot Cycle:
- Can determine the rate of rotation of the Sunfrom the measurement of
- Sunspot MovementGalileo was first to attempt to measure SolarRotation
- from his daily drawings of the sunspots
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Sunspot Cycle: a cycle of sunspots 11 yearsThe number of sunspots reaches a peak every 11 years
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Sunspot Cycle:Sunspot location also changes• ~30 degrees of Sun’s equator• spots move gradually towardSun’s equator
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Solar Rotation –
- varies between 25-35 days• the Sun is not asolid body like a ball•
- different partsrotate at differentrates• equator rotatesvery rapidly: 25
- days• poles take longer:35 days
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Sunspot features
Sunspots in pairs– positive andnegativeRegions ofintensemagnetic fieldCooler: 3-4000 K
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Sunspot Cycle
:Sunspot polarity also changes every ~11 years• North and South polarity reverse•total “Solar Cycle” is 22 years
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Chromosphere•
Thin layer above photosphere• 2000-3000 kmthick• 10,000 K
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Flares
Sudden eruptions ofenergy from SunLots of energy –billions of megatonsat a timeLots of radiation -Can be dangerousfor astronauts
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Solar Flares:
Larger “eruption” in Corona“eruptions” on the Sundue to:changes in the Sun’smagnetic field
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Prominences
• Gas held above sun’s surface by magnetic field• Can last minutes to months
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Corona:
million degree “halo” surrounding SunVery thin andtenuousVery hotVery large –extends millionsof miles intospace
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Corona changes structure duringsolar cycle
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Coronal loops:features are related to the Sun’s magnetic field
charged particles move with magnetic fields
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Layers of Sun’s atmosphere linkedto each other
Coronal loops coming out of sunspots
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Coronal Mass Ejections
Blast of gas moving out from the CoronaSpeeds as high as 1000 km/s50,000 km above the Sun’s surface
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Solar Wind
:the flow of gas from the Corona into spacemoves past Earth ~4 days after it leaves SunVan Allen Belts trap charged particles
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Helioseismology
The Sun “sings” and ringslike a bell
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