A modest G2 star, conveniently located 150,000,000 km from Earth.

The Sun

Solar Interior

The core is the energy source, where hydrogen fuses into helium.

Heat from the core spreads out through the radiative and convective zones.

How do we know...?

Neutrinos from nuclear fusion in the Sun’s core can be detected at Earth.

Sudbury Neutrino Observatory(Sky and Telescope)

How do we know...?

Helioseismology uses vibrations of the Sun’s surface to map its interior.

NJIT

Photosphere

The part we see! Nearly all the energy

from fusion is radiated into space from the photosphere.

Sunspots let us see rotation (27 days)

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are needed to see this picture.

SST (Royal Swedish Academy of Sciences)

Photosphere — Sunspots

SST (Royal Swedish Academy of Sciences)

What are Sunspots?

Strong magnetic fields coming up from the solar interior.

The field is strong enough to inhibit convection, so the surface cools & darkens.

They last from days to weeks, then fragment and spread out.

Chromosphere

Actually above the photosphere!

Seen by making images of spectral absorption lines

The structure reflects the Sun’s magnetic field.

Corona (solar eclipse)

What’s this? Sun’s outer

atmosphere Tenuous,

transparent Only one millionth

as bright as photosphere.

Corona in X-rays

Millions of degrees (much hotter than photosphere!)

Photosphere does not emit X-rays.

Coronal loops

TRACE

Filamentary structure traces the magnetic field

Temperatures

The power source is in the core (Temperature 15 MK).

Temperature decreases until we get to the photosphere (5800 K).

The chromosphere is hotter (up to 20,000K). Above this is a hot corona (1-10 MK) that

extends into space. What heats the corona? We think it’s the Sun’s magnetic field, but the

process is not well understood!

Corona compared to sunspots

Solar Cycle

Magnetic activity comes and goes on an 11-year cycle

11 year cycle

Coronal activity increases with the sunspots

1991 1995

High activity

Many sunspots Coronal mass

ejections Flares

Solar Flare

TRACE

Aurora Australis and Borealis

Earth’s magnetosphere

Low activity

Less x-rays produced

Fewer sunspots

Jupiter has a very large magnetosphere. Does it exhibit aurora?

A. Yes

B. No, its too far away

C. No, its not solid

D. Cannot conclude

Compare x-ray and visible

Movie

Sun

Layers: Corona Chromosphere Photosphere Core

Activity cycle Sunspots, mass ejections

You are making a mobile with a basketball for the Sun. What could you use for the other planets ? Sun: 1.4 million Km Mercury: 4,880 Km Venus: 12,100 Km Earth:12,756 Km Mars: 6,787 Km

Jupiter: 142,800 Km Saturn: 120,600 Km Uranus: 51,300 Km Neptune: 49,100 Km

SOHO