Announcements

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Slide 1

Announcements

Scores for first exam are available on WebCT.

Exams (A and B) with correct answers marked are available on usual course web site (not in WebCT).

Two more days of observing for extra credit for first exam.

Second exam will be on Friday, October 8th.

Fourth exam will be on Wednesday, Nov. 17, instead of Friday, Nov. 19.

Slide 2

Outer Layers of the Sun

Photosphere

Helioseismology

Sun spots

Chromosphere

Corona

Prominences, flares, coronal mass ejections

Reading 17.3-17.5

Slide 3

The Sun’s Atmosphere

Photosphere - the 5800 K layer we see.

Chromosphere – a thin layer, a few 1000 km thick, at a temperature of about 10,000 K. Can be seen during solar eclipse.

Corona – Outermost layer, 1,000,000 km thick, at a temperature of about 1,000,000 K.

Slide 4

Outer layers of sun

1 = photosphere, 2 = chromosphere, 3 = corona

Why the outer layers of the Sun’s atmosphere are hotter is a puzzle.

Slide 5

Photosphere

Slide 6

Chromosphere

Slide 7

Corona

Slide 8

Corona

Slide 9

The surface of the Sun vibrates up and down in oscillations which can go deep through the Sun.

We can observe these oscillations from Earth by looking at the Doppler shifts of different pieces of the Sun.

Helioseismology is a way to probe the Sun’s interior using the Sun’s own vibrations.

Slide 10

Limb darkening

Slide 11

Limb darkening

Slide 12

Sunspots are low temperature regions in the photosphere

Sun spots are about 4000 K (2000 K cooler than solar surface) and have magnetic fields up 1000 the normal solar magnetic field. They can be as large as 50,000 km and last for many months.

Slide 13

Particles spiral around magnetic field lines

Magnetic field