The Sun

Abundance of Elements in the Sun

Element % by Number % by MassHydrogen 92.0 73.4

Helium 7.8 25.0

Carbon 0.02 0.20

Nitrogen 0.008 0.09

Oxygen 0.06 0.8

Neon 0.01 0.16

Magnesium 0.003 0.06

Relative sizes

Visible sphere of the Sun

Earth

Structure of the Sun

What Makes the Sun to Shine?

Chemical Would only provide the necessary energy

for 3000 years

Gravitational Contraction Proposed by Helmholtz and Kelvin - would

power the Sun for a few hundred million years

By the early 1900’s geologists showed that the Earth is billions of years old.

Nuclear Energy

Fundamental Forces

Strong Nuclear Holds the nucleus of the atom together

Electromagnetic Responsible for all chemical reactions

Weak Nuclear Governs radioactive decay

Gravity

Proton-proton chain

Step 1

1H + 1H —> 2H + e+ + neutrino

Step 2

2H + 1H —> 3He + photon

2He+

3He

photon

4He

photon

1H

1H

Step 3

3He + 3He —> 4He +1H + 1H +photon

Hydrogen Fusion

Net result 4H --> He + e+ + + energy

Four protons are 0.7% more massive than one He

E = mc2

1.6 km

C2Cl4

Neutrino Telescope

Cosmic Rays

Ar

Argon Atom

100,000 gal. tank

Gold MineAr

Solar Neutrino Problem

Animation

Energy Transport

Conduction: the transfer of heat in a solid by collisions between atoms and/or molecules. Not applicable in stars

Radiation: the transfer of energy by electromagnetic waves. Inside the Sun and most stars, radiation is the principal means of heat transport.

Convection: the transfer of heat in a gas or liquid by means of the motion of the material.

McMath-Pierce Solar Telescope

Photosphere

Big Bear Solar Observatory

October 21, 2009

The Sharp Limb

Limit of resolution is one arcsec 700 km at 1 AU

Density falls very quickly in photosphere

Opaque here

Transparent here

Limb Darkening

Same 700 km penetration depth Viewed at disk center, light originates

deeper Temperature falls with height in

photosphere

Temperature of Photosphere

0

1000

2000

3000

4000

5000

6000

7000

0 500 1000

Height in Photosphere (km)

Tem

pera

ture

(K

)

Photosphere

Solar Spectrum

Granulation

Typically 1000 km across

Bright center, dark edge

Center moving out, edges moving in

The Movie

Granulation Convection

Hot Cool Hot

Chromosphere

Observing strategies During total eclipses

Chromosphere

Using spectroheliograph

H

Chromosphere

Supergranulation

Chromosphere

CaII

Spicules

Movie

The Corona

The quiet corona

The active corona

X-ray emission

The Movie

Solar Wind

Distance from photosphere

VelocityAverage particle

velocity

Escape Velocity

The Corona is Hot

The Corona is hot! X-ray emission Lines of highly ionized iron

• FeX, FeXIV, FeXV• Requires T 2,000,000 K

Coronal holes are the source of the Solar Wind

End of Section