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•Sunspots are the dark regions that appear on the surface of Sun.•The amount of solar activity on the Sun is not constant, and is closely related to the typical number of sunspots that are visible.•The number of sunspots and the levels of solar activity vary with an 11 year period known as the solar cycle.
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Solar Cycle:Solar Cycle:Number of spots = ~ 11 yrs
Magnetic polarity of spots = 22 years (to return to starting orientation)
Horace Babcock - Magnetic Dynamo via differential rotation
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Solar Solar Flares:Flares:The most violent events on the surface of the Sun are sudden eruptions called solar flares. Flares typically last a few minutes and can release energies equivalent to millions of hydrogen bombs.
Figure showing multiple solar flaresFigure showing multiple solar flares
It’s the sudden release of energy equal to 100s of millions of megatons - radio through gamma rays Temperatures exceed 10 million K
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Prominences - Prominences - filaments seen from the side.
•Quiescent Prominences
•Active Prominences
•Eruptive Prominences
Filaments - Filaments - cool streamers of gas above photosphere
Plages - Plages - heated by rising magnetic field - compresses gas
We see deeper when looking at the center of the “disk”
Brightness increases as T4 (Stefan-Boltzmann Law)11
Solar Solar WindWindOuter atmosphere is flowing away from the
Sun - the solar wind
Speeds up to few million km/hr
Earth is inside the solar wind!
At Earth:
V = 400 - 700 km/s
T = 50,000-500,000 K*
density = 103 - 104/m3
(Earth at sea level - ~2.5x1025/m3)
Solar wind expands outward,
creating the heliosphere12
Sunspots:
•Appear in groups
•T~4000-4500 K
•Darker than surrounding photosphere
•Large magnetic fields inhibit convection
umbra
penumbra
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Solar Magnetic Solar Magnetic Field:Field:
The heliospheric current sheet extends to the outer reaches of the Solar System, and results from the influence of the Sun's rotating magnetic field on the plasma in the interplanetary medium.