NOTES: The Sun How big? D(Jupiter) = 10 x D(Earth) D(Sun) = 10 x D(Jupiter) More precisely, D(Sun) = 109 x D(Earth). (See overlay) Or 1.3 million Earth volumes. How massive? M(Sun) = 330,000 M(Earth). How far? 1 AU = 1.5x108 km = 8.3 light mins (Pluto-5.5 lt hrs) How bright? Power output at source = Luminosity, L = 4 x watts. Enough power to cover surface with 100 watt tiny Christmas tree lights. How bright at Earth? Solar Constant = 1,370 watts/m 2. Like watt bulbs. Content? See abundance overlay.

How big? Roughly (diameters) D(Jupiter) = 10 x D(Earth) D(Sun) = 10 x D(Jupiter) More precisely, D(Sun) = 109 x D(Earth).

D(Sun) = 109 x D(Earth) Or 1.3 million Earth volumes.

How massive? M(Sun) = 330,000 M(Earth). Found using Newton’s version of Kepler’s 3 rd Law.

How far? 1 AU = 1.5x10 8 km = 8.3 light mins (Pluto-5.5 lt hrs) About 8,000 Pluto distances to the nearest star—Alpha Centauri

How bright at Earth? Solar Constant = 1,370 watts/m 2. Like watt bulbs. However, solar panels are less than 50% efficient. World’s largest solar facility—produces 150 megawatts. How many square meters could produce this?

Layers of the sun: Three means of energy transfer: Conduction (throughout), Convection, and Radiation. Photosphere: T= 5700 K Chromosphere T = 15,000 K Corona T = 2 million K

Radiation: high energy gamma rays emitted in core are absorbed and re-emitted as multiple photons, degrading energy. This is called the random walk. It takes 1-10 million years for energy to reach the sun's surface. Core: T = 15 million K

Source of Energy (Nuclear Fusion): P-P Process: Protons must have enough energy to overcome electric repulsion and fuse together. This means 10 million degrees K (Kelvin = Centigrade + 273). Dominates in stars less than 1.5 solar masses. p + p --> D + positron + neutrino p + D --> 3He + gamma ray 2 3He --> 4He + 2p

CNO Process: In stars above 1.5 solar masses there is recycled carbon in the core, which works as a catalyst for fusing protons into Helium 4. Catalyst: unchanged, but facilitates process.

Spectrum: Continuous spectrum with hundreds of dark lines. Peak wavelength gives surface temperature T = 5700 K of photosphere. We can see into various depths by looking out at toward the limb, or sun's edge.

Sunspots: Maximum every 11 years. 1.Sun's magn. pole also flips every 11 years.

They migrate toward equator.

We know we have intensified magnetic fields in sunspots by the amount certain spectral lines are split apart by the Zeeman effect.

No sunspots from AD--Maunder minimum. No one knows why, or whether it will happen again.

Sunspots are associated with flares, prominences, and coronal mass ejection.

Babcock's dynamo theory utilizes differential rotation to explain the variations in sunspots. It’s like a rubber band being wrapped around sun as it rotates. If will break eventually  solar minimum.

The solar wind of electrons (and a few protons) is increased during sunspot maximum and by solar flares.