Photons and the Solar Atmosphere

1. Photons and the Solar Atmosphere Lab 2

2. The Sun

3. Layers of the Sun Core temp 3x106 K

4. What happens in the core…. • In the core, fusion reactions produce energy in the form of gamma rays and neutrinos • γ rays are photons with high energy and high frequency. • These rays are absorbed and re-emitted by many atoms on their journey from the envelope to the outside of the sun. • When the γ rays leave atoms, their average energy is reduced • But by the first law of thermodynamics (which states that energy can neither be created nor be destroyed), the number of photons increases. • Each high-energy γ ray that leaves the solar envelope will eventually become a thousand low-energy photons

5. Solar Envelope The temperature is 4x106 K The density of the solar envelope is much less than that of the core. The core contains 40% of the sun's mass in 10% of the volume The solar envelope has 60% of the mass in 90% of the volume The solar envelope puts pressure on the core and maintains the core's temperature.

6. Photosphere • The photosphere is the zone from which the sunlight we see is emitted. • The photosphere is a comparatively thin layer of low pressure gases surrounding the envelope. • It is only a few 100 km thick, with a temperature of 6000 K.

7. Chromosphere • In an eclipse, a red circle around the outside of the sun can sometimes can be seen • Its red coloring is caused by the abundance of hydrogen. • From the center of the sun to the chromosphere, the temperature decreases proportionally as the distance from the core increases. • The chromosphere's temperature is 7000 K, hotter than that of the photosphere. • Temperatures continue to increase through the corona.

8. Corona • The outermost layer of the sun is the corona. • Only visible during eclipses, it is a low density cloud of plasma with higher transparency than the inner layers. • The white corona is a million times less bright than the inner layers of the sun, but is many times larger. • The corona is hotter than some of the inner layers. • Its average temperature is 1x106 K but in some places it can reach 3x106 K • Temperatures steadily decrease as we move farther away from the core, but after the photosphere they begin to rise again.

9. eV in every day terms • An eV is an electron volt.  It is defined as the amount of energy acquired by an electron as it accelerates across a voltage difference of 1 volt.  Remember, electrons are charged particles, and electricity is just movement of electrons from a negatively charged point to a positively charged point. • How much is one eV?  Very small.  1 eV = 3.88x10^-20 calories.  To put it in perspective, one teaspoon of sugar has 20,000 calories. • In the Sun's core, hydrogen is busily fusing into helium.  4 hydrogen atoms fuse to become 1 helium atom.  The energy released by 1 gram of hydrogen when fused to form helium is 1.5x10^11 calories.  Not small. • Comparatively speaking, if we burn 1 gram of hydrogen with oxygen to get water, we only release 3x10^4 calories.  Small.