Photons and the Solar Atmosphere

Lab 2

The Sun

Layers of the Sun

Core temp 3x106 K

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

Solar Envelope

The temperature is 4x106 KThe 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 volumeThe solar envelope has 60% of the mass in

90% of the volumeThe solar envelope puts pressure on the

core and maintains the core's temperature.

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.

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.

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.

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.