Sun

Our sun. It is the one focal point in our solar system that everything is measured by. Solar time, noon, 4pm, 3am, it is all measured by the sun. The sun causes our crops to grow, provides us with the heat and light that is necessary for life to exist, and keeps all of the planets in orbit with its gravity. But what is really going on with our nearest star?

In the days of ancient mythology it was thought that the sun was really a god called Apollo who rode his chariot across the sky each day and brought light and heat to the earth. It has also been thought that the earth was stationary, and all the other planets orbited around it. But now, with the aid of telescopes and mathematics, we know that this is not the way it is.

The sun is a giant sphere consisting of at least three-fourths hydrogen, and one-fourth helium. Of the 109 elements known to us, at least 70 have been found in the sun. But all of these elements combined only makes up between 1 or 2 percent of the sun's mass.

The mass of the sun is about 1,047 times that of Jupiter. And it would take 333,000 planets of Earth's size to come close to equaling the sun's mass. Because of this mass, the force of gravity on the sun is much greater than it is on any of the other planets. If we were to send something to the sun that weighs100 pounds, and were to weigh it there, it would not weigh 100 pounds, but 2,800 pounds. It is the force of this gravity that keeps the gasses of the sun from escaping into space. But if there were nothing to balance out the force of gravity on the sun, it would collapse. The gasses of the sun are extremely hot and want to expand out into space, but the gravity keeps them from doing so. It is this combination that keeps the sun from losing itself into space.

Astronomers can not, of course, go to the sun and measure its heat directly. Instead, they determine it from measurements of sunlight and mathematical equations that are based on known physical laws. Astronomers have in this way been able to determine the center of the sun to be about 27,000,000 degrees F. (15,000,000 degrees C). Since the sun's energy is produced at its center and gradually flows to the surface, the sun's surface isn't going to be as hot as the center. At the sun's surface, the temperature is only about 10,000 degrees F. (5500 degrees C). Midway between the center and the surface the sun cooks at about 4,500,000 degrees F. (2,500,000 degrees C).

It was once thought that the heat produced by the sun came from something that was burning. But today scientists know that the sun's heat and light come from thermonuclear reactions in its center. Thermonuclear reactions are the combination or fusion of four hydrogen atoms to produce one helium atom. This end product is lighter than the four hydrogen atoms, and as a consequence, energy is liberated. This is where the sun gets its power.

When changes occur in the magnetic field of the sun, sunspots, flares, prominences, and other stormy activities start appearing.

Sunspots occur when the magnetic lines of the sun cross through the surface and lower the temperature of the surrounding gas. This gas doesn't shine as bright as the gas around it, and it appears as a sunspot.

Flares occur after a sunspot group has existed for a long time. The magnetic lines become jumbled, and as a result magnetic energy becomes stored in the corona. To release this energy and bring the magnetic lines back into place, the sun releases energy in the form of light, heat, and fast-moving atomic nuclei and electrons called solar cosmic rays. These rays can very greatly in size.

Prominences are bright arches of gas outlining long, strong bundles of magnetic lines of force. Prominences shine brightly because the gasses they are made of are more dense and radiate light more efficiently than do the gasses in the chromosphere and the corona. These prominences can be 20,000 miles (32,000 kilometers) high, and can either be quiescent, or active. Quiescent prominences don't change much during their two or three month life. Active ones, on the other hand, can change form rapidly in the period of an hour or so.

The word chromosphere means 'colored zone.' It is the middle region of the sun's atmosphere. We can see the chromosphere for a few seconds as the magenta fringe at the beginning and end of a total eclipse.

The corona is the area just outside of the chromosphere. It is the outermost atmosphere surrounding the sun. In a total eclipse the corona can be seen as a great crown around the sun. The corona's high temperature is about 4,000,000 degrees F. (2,200,000 degrees C.)

The solar wind is a continuous flow of gasses coming from the sun. It is caused chiefly by the expansion of gasses in the corona. The high temperatures found in the corona heat the gasses and cause them to expand and collide. As they collide they lose their electrons and become ions. This is what makes up the solar wind.

Fact Sheet
Name		Sun
Latin Name/Greek Name		Sol/Helios
Symbol
Year Discovered/Discoverer		N/A
Mass		1,989,100 x 10²⁴ kg
Volume		1,412,000 x 10¹² km³
Density		1408 kg/m³
Surface Gravity		274.0 m/s²
Escape Velocity		617.7 km/s
Volumetric Mean Radius		696,000 km
Motion
	Sidereal Rotation Period (Earth Hours)	609.12
	Rotation Direction	Direct
	Inclination of Equator to Ecliptic	7.25 degrees
Natural Satellites		Mercury Venus Earth Mars Asteroids Jupiter Saturn Uranus Neptune Pluto

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