The Sun - Our Star

Mass = 1.9889x10³⁰kg = 0.333x10⁶ Earth Masses

Radius = 6.960x10⁵km = 109 Earth Radii

Distance = 1.496x10⁸km = 1AU = 8 light-minutes

Surface Temperature = 5,800K

Central Temperature = 15,000,000 K

Period of rotation = 25 days at equator

The sun is a star no different that any other star in the night sky, except that it is much nearer. Like most stars the sun is a ball of hot gases - with 76% of its mass being Hydrogen and the rest being mostly Helium. Thus, the sun - eventhough extremely massive - is made out of the two lightest elements in the periodic table. Apparent only during a total eclipse, the sun's outer most layer, the corona, streams out from over the visible yellow disk of the photosphere. The temperature in the rarefied gas of the corona is millions of degrees. Between the photosphere and the corona, the chromosphere is seen as a layer of pink blowing flames.

Solar Atmosphere Temperature Radiation

Photosphere (5,000-6,000)K 500-600 nm - Visible

Chromosphere (10,000-500,000)K 6-300 nm -UV

Corona (500,000-2,000,000)K 1-6 nm - UV

How are the chromosphere and corona heated to such high temperatures remains a mistery!!

How are the chromosphere and corona heated to such high temperatures remains a mistery!!
Solar Atmosphere	Temperature	Radiation
Photosphere	(5,000-6,000)K	500-600 nm - Visible
Chromosphere	(10,000-500,000)K	6-300 nm -UV
Corona	(500,000-2,000,000)K	1-6 nm - UV

We know that the gravitational force - the force acting between massive objects - is responsible for holding planets moving in elliptical orbits around the sun. We also know that the electromagnetic force, the force acting between charges and magnets , is responsible for holding electrons moving in discrete orbits around the atomic nucleus. But if the nucleus is made out of protons (charged particles) and neutrons (which carry no electric charge) what force keeps neutrons and protons bound to the nucleus?

The sun's power house is buried in its central core. There, the temperature is 15 million degrees and the gas (Hydrogen and Helium) is 20 time denser than iron. Hydrogen nuclei (76% of the Sun) are single protons that overcome their electrostatic repulsion and collide hard together to build up into nuclei of helium. A Helium nucleus is slightly lighter than four protons, so the excess mass is converted into energy according to one of the most famous physics formulas of all time: Einstein's E=Mc² Every second four million tons of hydrogen vanish to generate the sun's energy. This energy radiates outward from the core.

The Majestic Sun

Explanation: Sometimes, small regions of the Sun appear unusually dark. Visible above is a close-up picture of a sunspot, a depression on the Sun's face that is slightly cooler and less luminous than the rest of the Sun. The Sun's complex magnetic field creates this cool region by inhibiting hot material from entering the spot. Sunspots can be larger than the Earth and typically last for only a few days. This high-resolution picture also shows clearly that the Sun's face is a bubbling sea of separate cells of hot gas. These cells are known as granules. A solar granule is about 100
One kilogram of Hydrogen - which the Sun has 10³⁰ of them - releases 100 million kilowatts-hour. Note that taking away 1 kg from the Sun "affects" the Sun much less than removing a drop of water from all the Oceans of the world combined. With this amount of energy you can:

         a) Power 60 million light bulbs for a full day
         b) Power 600 light bulbs for a full day in every house in Tallahassee
         c) Power all of Tallahassee for about one month

The Dynamic Sun

IIn the layers just below the photosphere blowing rows of gas rise to the surface, then fall again as they cool. Good photographs show that the sun's surface is not uniform but it is filled with dark-edged bright cells. These cells are formed from gas bubbling up to create a pattern called granulation. Each cell is hundreds of miles across. Jets of gas called spicules shoot up like flames thousands of miles high. In disturbed regions sunspots appear often in groups or pairs. Sunspots look dark because they are several thousands of degrees cooler than their surroundings. Huge prominences, vastest than the whole of the earth, can erupt from active areas of the sun. The most intense bursts of energy in active regions are solar flares. They can blast atomic particles as far as the earth and beyond. These particles add to the gas constantly streaming away from the sun into the solar system as the solar wind. The earth's magnetic field funnels particles from the sun downwards near the north and south pole. These particles crush into the upper atmosphere making it glow with the aurora. The sun has its own magnetic field which is about 5 times stronger than the earth's. The sun's magnetism controls the appearance of sunspots and many other solar phenomena.

The sun spins about once a month but the rate varies with latitude. This is called differential rotation. Each magnetic field line is tied into the fabric of the sun. As the sun turns the field gets more and more wound up and distorted. Sunspots form where the field lines loop out through the surface. In the end the twisted pattern breaks down and then the regular field takes over. This lasts about 11 years the length of the sunspot cycle. At sunspot minimum there are very few spots and they appear near the sun's equator. Individual spots last a few weeks at most but the overall number of spots and the places they appear both change as the cycle progresses. New spots come at high latitudes both north and south. After a few years the number of spots appearing reaches a peak and they are mostly in bands about 20 degrees both north and south of the equator. Then activity declines until the whole natural cycle recurs once more.