Solar System/Sun

''This page is about the Sun. To learn more about the Solar System general competition, go to the main Solar System page.''

The Sun
The Sun is the largest body in our solar system, and contains 99.8% of the mass. Because it is a globe of gases, it rotates differently depending on the area. The equator takes around 25 days, whereas the polar regions take around 35 days (Earth days). It is 4.6 billion years old and is made up of layers, starting from the outside(with Temperatures), Corona(1,000,000 C), Transitive Region, Chromosphere, Photosphere(6,000 C), Convection Zone(1,000,000 C), Radiative Zone(2,000,000 C),and the Core(15,000,000 C).It produces heat from the fusion of hydrogen atoms. The heat is transferred by the process of convection, through the radiative and the convective zone, where it is radiated out through the photosphere and corona to the planets in the form of rays.

Core
The core is the densest part of the sun, with a density of 160 g/cm^3. That is ten times that of lead, 160 that of water, or about 250 billion atmospheres. Although, the temperature is 15 million kelvin, or 27 million degrees Fahrenheit, which keeps the core in a gaseous state. The core is where fusion takes place. Fusion is the process of small molecules combining to form larger ones, releasing energy. The force of gravity is so strong that it breaks down atoms into protons, neutrons, and electrons. Sometimes protons will combine with neutrons to form deuterons. If these deuterons combine with one more proton, they form a helium-3 isotope. Two of these combine to make a helium atom. The missing proton (remember that the helium-3 isotope has 1 neutron and 2 protons each) is released in the form of energy. Every second, about 700 million tons of hydrogen are converted to 695 million tons of helium and 5 million tons of energy in the form of gamma rays. The energy generated in the core of the Sun takes a million years to reach the surface of the Sun.

Radiative Zone
Surounding the core is the radiative zone. This area is hot and dense that energy from the core can radiate outwards through this area. Ions of helium and hydrogen emit photons, which then get absorbed by more hydrogen and helium isotopes. Basically, light energy bounces from particle to particle. Photons travel slowly this way. It can take 100,000 years for a single photon to exit the radiative zone.

Convection zone
The sun isn't hot enough in this outer layer to radiate through here, but instead the energy moves through here through convection, or the process of hotter things rising and cooler things falling. The solar plasma here heats up as you get closer to the core, rising, lets out the energy near the top, then falls again. The convection zone is from about 200,000 km deep to the "visible surface" of the Sun.

Photosphere
The outermost part of the sun is called the photosphere. This is where the energy made in the core is finally released into the sun's atmosphere. This is the visible part of the sun. Sunspot are "cool" regions of the photosphere.

Chromosphere
Above the photosphere, the chromosphere is almost transparent, but it can be seen as a thin red glow around the Sun during a Solar Eclipse. Solar flares also take place in the Chromosphere. The temperature here rises from about 4600 K at the part closest to the photosphere to about 8600 K at the outer edge. It is about 2,000 km deep.

Transitive Region
Helium becomes fully ionized, which leads to worse heat conduction and skyrocketing temperatures. Also, this is where magnetic forces start to determine how solar structures look and act instead of gas pressure and fluid dynamics. Below the transitive region, solar emissions are largely in infrared, visible light, and near ultraviolet. At or above the trasitive region, emissions tend to be in far UV or X-rays.

Corona
A type of plasma "atmosphere" that extends hundreds of kilometers into space. However, the corona is only visible during a total Solar Eclipse. The light that can be seen from the corona comes from light bouncing off free electrons (K-corona, "k" for kontinuierlich or continuous), light bouncing off dust particles (F-corona, "f" for Fraunhofer, a German physicist who discovered certain spectral lines in sunlight), and ions present in the corona's plasma (E-corona, "e" for emissions from the ions). The word corona is derived from the Latin word for "crown".

Solar Features
Prominence- These large bright solar features extend outwards from the sun's photosphere into its corona, often in the shape of a loop. Typically, prominence loops are many times the size of the earth. They are more common at the height of the solar cycle, when the sun's magnetic field has become tangled and strong magnetic loops extend into its atmosphere, bringing ionized hydrogen gas with it. Prominences decrease in number as the magnetic field sorts itself out into simpler arrangements. They are made up of plasma, just like the corona (only much cooler), and evolve from day to day because of the instability of the magnetic field. The more stable prominences can last for several days or weeks while the more violent ones only last several hours. Some of them break up as the loop expands (the pressure of the hydrogen gas increases until it's enough to break through the field) and produce coronal mass ejections.

Filament- A prominence seen with the sun behind it rather than open space. Filaments appear darker than the rest of the sun.

Spicule- These small, jet-like eruptions on the sun's surface appear as dark streaks. Spicules only last a few minutes, but they eject material outwards into the corona at 20-30 km/s.

Flare- Flares are sudden, intense variations in the brightness of the sun- basically an explosion resulting from stored energy being released into space. They accelerate electrons, protons, and ions to almost light-speed and heat plasma to tens of millions of Kelvins. The resulting radiation is visible across the whole electromagnetic spectrum, from radio waves through visible light to gamma rays. They tend to occur near sunspots between opposing magnetic fields.

Sunspot- Sunspots are "cool" (about 3800 K) areas of the Sun's surface. They appear dark in comparison with the rest of the photosphere. No one really knows what causes sunspots, although it is thought that they result from complicated interactions within the Sun's magnetic field.

Solar Wind- A low density stream of photons and electrons that moves throughout the solar system and about 450 km/sec. During the minimum of the solar cycle, the solar wind flows much faster (750 km/sec) at the Sun's poles than it does closer to the equator. When the solar cycle is at its maximum, the solar wind flows at a much more constant speed. In the late 1600s, a period of low sunspot activity, called the Maunder Minimum, coincided with the "Little Ice Age" in Europe- a time of abnormally low temperatures.

Coronal Mass Ejection- Large bubbles of gases following magnetic field lines that are ejected from the sun over the course of several hours. They produce disturbances in the solar wind that can issues with telecommunications on Earth as well as other adverse effects. CMEs are often associated with solar flares and prominences.

Granules- Small convection cells of really hot solar gas on the surface of the sun.

Links
More sun numbers

main Solar System page.