Solar Page

Photo-Sunset

The Sun

All the stars, including our Sun, are gigantic balls of superheated gas, kept hot by atomic reactions in their centers. In our Sun, this atomic reaction is hydrogen fusion: four hydrogen atoms are combined to form one helium atom. The temperature at the core of our Sun must be 20 million degrees centigrade, and the surface temperature averages 6,000 Deg C, or about 11,000 Deg F. The diameter of the Sun is 865,400 miles, and its surface area is approximately 12,000 times that of Earth. Compared with other stars, our Sun is just a bit below average in size and temperature, and is a yellow dwarf star. Its fuel supply (hydrogen) is estimated to be sufficient for another 5 billion years.

Rotation

Our Sun is not motionless in space; in fact it has two proper motions. One is a seemingly straight-line motion in the direction of the constellation Hercules at the rate of about 12 miles per second. But since the Sun is a part of the Milky Way system and since the whole system rotates slowly around its own center, the Sun also moves at the rate of 175 miles per second as part of the rotating Milky Way system. In addition to this motion, the Sun rotates on its axis. Observing the motion of sunspots (darkish areas that look like enormous whirling storms) and solar flares, which are usually associated with sunspots, has shown that the rotational period of the Sun is just short of 25 days. But this figure is valid for the Sun's equator only; the sections near the Sun's poles seem to have a rotational period of 34 days. Naturally, since the Sun generates its own heat and light, there is no temperature difference between poles and equator. In 1998, scientists saw for the first time that solar flares produce seismic waves in the Sun's interior that resemble those created by earthquakes. They observed a flare-generated solar quake equivalent to a 11.3 magnitude earthquake. It contained about 40,000 times the energy released in the great 1906 San Francisco earthquake.

Solar Cycle

The Sun is like a giant nuclear reactor, made up mostly of electrically charged Hydrogen and Helium gas and the temperature at the core is around 15,000,000 Deg C. The Sun is not a solid body, but a jelly like mass, and the surface, or Photosphere rotates once every 25 days at the equator, once in 28 days at latitude 45 Deg and once in 34 days near the poles, so you can see that the poles are continually being lapped by the equator, causing the magnetic field, carried by the Plasma (electrically charged gas), to wind itself up as the Sun rotates. After an approximate 11 year cycle, the magnetic field lines short circuit and the field strength falls; in turn the whole field reverses polarity and a new cycle begins. An 11 year cycle is the average, but a cycle can be as short as 5 years, or as long as 16 years.

Solar Flares

As the Sun's magnetic field is being wound up, an immense amount of energy is stored and local field strengths are increased as they are attempting to repel each other. Eventually, the repulsion between the lines become strong enough to overcome gravity and mixed with the Plasma, in their fury, they will burst through the Photosphere (surface). Sometime later the Sunspots will be visible and because they are much cooler than the Photosphere, they show up as much darker areas. At the Solar maximum when these events occur, Sunspots are at their peak and most aggressive and the ultra violet rays from the Flares are most intense, causing excessive ionization of the ionosphere. Solar Flares often reach earth, carried by the Solar wind (energy escaping from the Sun towards earth) and by increased ionization of the ionospheres layers, can affect propagation in many different ways and can cause problems here on earth when it reaches earth's magnetic field.

Photosphere

What we call the Sun's surface is technically known as the photosphere. Since the whole Sun is a ball of very hot gas, there is really no such thing as a surface; it is a question of visual impression. The next layer outside the photosphere is known as the Chromosphere, which extends several thousand miles beyond the photosphere. It is in steady motion, and often enormous prominences can be seen to burst from it, extending as much as 100,000 miles into space. Outside the Chromosphere is the corona. The corona consists of very tenuous gases (essentially hydrogen) and makes a magnificent sight when the Sun is eclipsed.

The End

As the Sun ages, it gradually expands and heats. In 1994, American astrophysicists studying the eventual fate of the Sun estimated that its brilliancy will increase by 10% over the next 1.1 billion years or more and, in about 6.5 billion years hence, our aging star will have doubled its present luminosity. The extreme heat generated will cause a catastrophic greenhouse effect on Earth and our oceans will boil away, and life on Earth as we know it will end. The Sun will eventually expand enormously to 166 times its present size and become over 2,000 times as bright. Eight billion years from now, the Sun's radius will engulf the planet Mercury and extend beyond the present orbit of Venus, causing the total destruction of the Earth. The Sun is the closest star to the earth, approximately 93,000,000 miles away and the end of its influence extends well beyond the orbit of Pluto 3,765,000,000 miles away. It has been shining for 4.6 billion years and will shine for another 4.4 billion years before starting its death. It uses up its nuclear fuel at a rate of 7 million tons per second.