The Sun

Not an "Ordinary" Star

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What is the Sun?

"The Sun is the star at the center of the Solar System and is by far the most important source of energy for life on Earth."

The Layers of the Sun

The Core

"The Sun's core is the central region where nuclear reactions consume hydrogen to form helium. These reactions release the energy that ultimately leaves the surface as visible light. These reactions are highly sensitive to temperature and density. The individual hydrogen nuclei must collide with enough energy to give a reasonable probability of overcoming the repulsive electrical force between these two positively charged particles. The temperature at the very center of the Sun is about 15,000,000° C (27,000,000° F) and the density is about 150 g/cm³ (approximately 10 times the density of gold, 19.3 g/cm³ or lead, 11.3 g/cm³). Both the temperature and the density decrease as one moves outward from the center of the Sun. The nuclear burning is almost completely shut off beyond the outer edge of the core (about 25% of the distance to the surface or 175,000 km from the center). At that point, the temperature is only half its central value and the density drops to about 20 g/cm³. "


The Radioactive Zone


"The radiative zone extends outward from the outer edge of the core to the interface layer or tachocline at the base of the convection zone (from 25% of the distance to the surface to 70% of that distance). The radiative zone is characterized by the method of energy transport - radiation. The energy generated in the core is carried by light (photons) that bounces from particle to particle through the radiative zone.

Although the photons travel at the speed of light, they bounce so many times through this dense material that an individual photon takes about a million years to finally reach the interface layer. The density drops from 20 g/cm³ (about the density of gold) down to only 0.2 g/cm³ (less than the density of water) from the bottom to the top of the radiative zone. The temperature falls from 7,000,000° C to about 2,000,000° C over the same distance."


The Convective Layer


"A layer in a star in which convection currents are the main mechanism by which energy is transported outward. In the Sun, a convection zone extends from just below the photosphere to about seventy percent of the solar radius."


The Photosphere

"The material that reaches the top of the convection zone cools by giving of light. This region of the Sun is the first part of the Sun that is visible to us and we call it the photosphere. This is where the light we see from the Sun originates. If we could look at the Sun directly (never stare at the Sun without the proper equipment) we would see the photosphere. Even though the layer is not solid we call this part of the Sun the surface and it is also where the solar atmosphere starts. Its temperature is around 5,800 Celsius or 10,000 degrees Fahrenheit."


The Chromosphere

Above the photosphere is a layer of the atmosphere about 2,000 km thick called the chromosphere. The temperature increases as you move higher to about 20,000 degrees Celsius at the top of the chromosphere. The chromosphere is no longer white light like the photosphere but is mostly red in visible light. It can be seen as red flashes during a total solar eclipse.


Corona

"The highest part of the solar atmosphere is called the corona. The corona starts around 10,000 km above the solar photosphere. Unlike the atmosphere of the Earth the atmosphere of the Sun continues to get hotter as you move away from the solar surface. The answer of why exactly this happens is one of the biggest questions of astronomy and solar physics of the 20th and 21st centuries. At 20,000-25,000 km away from the solar surface the corona has an average temperature of 1,000,000 to 2,000,000 million degrees Celsius. But the density is very low, about 1 billion times less dense than water."

Sunspots

The sun is a "spot or patch appearing from time to time on the sun's surface, appearing dark by contrast with its surroundings."

Prominence

"A prominence is a large, bright, gaseous feature extending outward from the Sun's surface, often in a loop shape. Prominences are anchored to the Sun's surface in the photosphere and extend outwards into the Sun's corona. While the corona consists of extremely hot ionized gasses, known as plasma, which do not emit much visible light, prominences contain much cooler plasma, similar in composition to that of the chromosphere. The prominence plasma is typically a hundred times cooler and denser than the coronal plasma. A prominence forms over timescales of about a day, and prominences may persist in the corona for several weeks or months. Some prominences break apart and may then give rise to coronal mass ejections. Scientists are currently researching how and why prominences are formed.


A prominence forms over timescales of about a day, and stable prominences may persist in the corona for several months, looping hundreds of thousands of miles into space.


The red-glowing looped material is plasma, a hot gas composed of electrically charged hydrogen and helium. The prominence plasma flows along a tangled and twisted structure of magnetic fields generated by the sun’s internal dynamo. An erupting prominence occurs when such a structure becomes unstable and bursts outward, releasing the plasma.


A typical prominence extends over many thousands of kilometers; the largest on record was estimated at over 800,000 kilometers "A prominence is a large, bright, gaseous feature extending outward from the Sun's surface, often in a loop shape. Prominences are anchored to the Sun's surface in the photosphere and extend outwards into the Sun's corona. While the corona consists of extremely hot ionized gasses, known as plasma, which do not emit much visible light, prominences contain much cooler plasma, similar in composition to that of the chromosphere. The prominence plasma is typically a hundred times cooler and denser than the coronal plasma. A prominence forms over timescales of about a day, and prominences may persist in the corona for several weeks or months. Some prominences break apart and may then give rise to coronal mass ejections. Scientists are currently researching how and why prominences are formed.

A prominence forms over timescales of about a day, and stable prominences may persist in the corona for several months, looping hundreds of thousands of miles into space.

The red-glowing looped material is plasma, a hot gas composed of electrically charged hydrogen and helium. The prominence plasma flows along a tangled and twisted structure of magnetic fields generated by the sun’s internal dynamo. An erupting prominence occurs when such a structure becomes unstable and bursts outward, releasing the plasma.

A typical prominence extends over many thousands of kilometers; the largest on record was estimated at over 800,000 kilometers "

Flares

"A flare is defined as a sudden, rapid, and intense variation in brightness. A solar flare occurs when magnetic energy that has built up in the solar atmosphere is suddenly released. Radiation is emitted across virtually the entire electromagnetic spectrum, from radio waves at the long wavelength end, through optical emission to x-rays and gamma rays at the short wavelength end. The amount of energy released is the equivalent of millions of 100-megaton hydrogen bombs exploding at the same time! The first solar flare recorded in astronomical literature was on September 1, 1859. Two scientists, Richard C. Carrington and Richard Hodgson, were independently observing sunspots at the time when they viewed a large flare in white light."

Aurora

"Aurora are one effect of such energetic particles, which can speed out from the sun both in a steady stream called the solar wind and due to giant eruptions are known as coronal mass ejections or CMEs. After a trip toward Earth that can last two to three days, the solar particles and magnetic fields cause the release of particles already trapped near Earth, which in turn trigger reactions in the upper atmosphere in which oxygen and nitrogen molecules release photons of light. The result: the Northern and Southern lights."