Our Star The Sun

Sun Statistics Radius: 700,000 km 109 Earth Radii Mass: 2 x 10^30 Kg 333,000 Earth Masses Density: 1.4 g/cm³ on average, increases greatly with depth to 150 g/cm³ Surface Temperature: 5780º K (9900º F) Core Temperature: 15,000,000°K Composition: Gas; 71% Hydrogen, 27% Helium, 2% Other heavier elements. Power Output: 4 x 10^26 watts

The Sun, an Energy Source The Sun is the source of nearly all energy on Earth. (Exceptions?) The source of this energy lies in the Core. There Fusion reactions turn hydrogen into helium releasing energy. The energy then starts it journey out, and to Earth, etc. First it passes through the Radiative Zone, where photons are emitted, absorbed and re-emitted by atoms. Then it passes through the Convection Zone, there it is carried by rising currents to the Photosphere. It is the thin Photosphere that radiates the light that we see and feel on Earth.

Inner Layers of the Sun Core: out to .3R 15-8 million °K Radiative Zone: .3R --.7R 8-2 million °K Convection Zone .7 -- .99 R 2 million °K to 6000 °K Photosphere 5780 °K

Granulation Granulation is when Rising Convection Currents make photosphere look like glowing grains called granules.

The center of the granules are where the currents rise. They glow brightly yellow with the heat carried up The edges are where the currents go back down. There it is cooler and thus darker and redder.

Layers of the Sun’s Atmosphere The Chromosphere is the dim lowest layer of the Sun’s atmosphere. It & the Corona are only visible during an eclipse. It is colored red because it is cooler at 4500ºK It consists of spiky Spicules, jets of gas thousands of kilometers long. Temperatures begin to rise at 2000 km out. The Corona is the outer layer of the Sun’s atmosphere. It glows blue-white because its temperature reaches 50,000°K. It extends out 100’s thousands of km.

Hydrostatic Equilibrium The gravity of the mass of the Sun creates great pressure and thus density. This pressure pushes inward creating the heat that makes the fusion in the core possible. But The fusion creates forces that push back out against the pressure. These forces balance making the “Hydrostatic Equilibrium” that keeps the Sun the size it is.

How do we know all this? The color of the light tells us the temperature of the Photosphere, Chromosphere, and Corona When fusion occurs particles called neutrinos are released that travel out from the core. By counting them we can calculate the rate of Fusion. Absorption/emission spectra tell us what its made of. Finally Solar Seismology studies “Sunquakes” to understand the Sun’s interior.