The Sun

Abundance of Elements in the Sun Element% by Number% by Mass Hydrogen Helium Carbon Nitrogen Oxygen Neon Magnesium

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 1 H + 1 H —> 2 H + e + + neutrino Step 2 2 H + 1 H —> 3 He + photon 2H2H e+e+ 3 He photon 4 He photon 1H1H 1H1H Step 3 3 He + 3 He —> 4 He + 1 H + 1 H +photon

Hydrogen Fusion  Net result  4H --> He + e energy  Four protons are 0.7% more massive than one He E = mc 2

1.6 km C 2 Cl 4 Neutrino Telescope Cosmic Rays Ar Argon Atom 100,000 gal. tank Gold Mine Ar

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 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 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 Velocity Average 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

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