Classroom Presentation about the Sun

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§ Dark regions are where cooler material is sinking.

§ Material rises/sinks @ ~1 km/sec (2200 mph; Doppler).

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The Solar Atmosphere

§ The solar spectrum has thousands of absorption lines

§ More than 67 different elements are present!

§ Hydrogen is the most abundant element followed by Helium (1st discovered in the Sun!)

Spectral lines only tell us about the part of the Sun that forms them (photosphere and chromosphere) but these elements are also thought to be representative of the entire Sun.

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Chromosphere

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Chromosphere (seen during full Solar eclipse)

§ Chromosphere emits very little light because it is of low density

§ Reddish hue due to 3®2 (656.3 nm) line emission from Hydrogen

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SOHO SPECTROHELIOGRAMS TODAY

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Solar Wind

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Solar Wind

v Coronal gas has enough heat (kinetic) energy to escape the Sun’s gravity.

v The Sun is evaporating via this “wind”.

vSolar wind travels at ~500 km/s, reaching Earth in ~3 days

v The Sun loses about 1 million tons of matter each second!

vHowever, over the Sun’s lifetime, it has lost only ~0.1% of its total mass.

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Hot coronal gas (~1,000,000 K) emits mostly in X-rays.

Coronal holes are sources of the solar wind (lower density regions)

Coronal holes are related to the Sun’s magnetic field

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The Active Sun

Most of theSolar luminosity is continuous photosphere emission.

But, there is an irregular component

(contributing little to the Sun’s total luminosity).

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Sunspots

Granulation around sunspot

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