General Solar Information

The composition of the Sun is primarily hydrogen, followed by rapidly decreasing amounts of almost every element. Below is a list showing the fractional amounts of the most common elements.

         0.9396  hydrogen
        0.05919  helium
      0.0006483  oxygen
      0.0003946  carbon
      0.0000817  nitrogen
      0.0000423  silicon
      0.0000376  magnesium
      0.0000348  neon
      0.0000301  iron
      0.0000150  sulfur
      0.0000028  aluminum
      0.0000019  calcium
      0.0000019  sodium
      0.0000019  nickel
      0.0000009  argon
    

The distance from the Earth to the Sun varies throughout the year. At perihelion (closest approach) the distance is 147 million km, and at aphelion (farthest) the distance is 152 million km. Due to this distance variation, the Sun will appear about 3% bigger at perihelion than at aphelion. At this point in geological time, perihelion occurs in early January, and aphelion in early July. Slowly but surely, however, the perihelion point precesses, so in 23,000 or so years, perihelion will occur in July.

Note that the Earth's seasons are due to the inclination of the Earth's equator with respect to the Earth's orbital plane, which is about 23 degrees. The Earth-Sun distance variation has only an incredibly small effect in temperature. Here's a way you can test this. Put yourself about 152 feet away from a friend, and then have them yell at you. Then, move 5 feet (3%) closer, and have them yell again. You will notice almost no difference in how loud they sound. (The metric equivalent is: 46 meters away, and then 1.5 meters closer.)

The Sun's age is estimated to be around 4.5 billion years. It should remain more or less as it is for another 5.5 billion years, although it will continually be undergoing changes as it consumes its fuel through fusion.

On an more timely basis, the Sun often undergoes rapid magnetic field reconfigurations. When this occurs, large amounts of material are ejected into interplanetary space. These events are called Coronal Mass Ejections or CMEs. A large CME will carry a million tons of material out towards the planets at a million miles an hour. (Almost a billion kg at 27 million m/s.) When a portion of this material reaches the Earth's outer atmosphere, it impacts satellites, perturbing their orbits, scoring their surfaces, and disrupting communications. The solar material can slide down the Earth's magnetic field lines and cause the phenomenon known as Aurora, and also burn out and totally disrupt power grids.

CMEs occur perhaps once a month or so during solar minimum, and up to twice or more a day at solar maximum. The Sun's most recent max was in 1989 and the next will be in approximately 2000. It is now approaching minimum which should occur in mid-1996.

Solar max and min referred initially to the number of sunspots observed on the surface of the Sun at any time. The number of sunspots is closely related to the complexity of the Sun's magnetic field that extends past its surface. The more complex the field, the higher the number of sunspots, and the higher the activity of CMEs and flares. There is some variation, but typically there are 11 years from one maximum to the next maximum.

In addition, the rotation of the interior of the Sun is very important to the existence of the magnetic field. Since one cannot see the interior of the Sun, one must use indirect methods. As everyone knows, if one strikes an object, one can tell something about its substance by the way it vibrates in response. For example, a bell will ring, and jello will just wiggle. The same applies to the Sun. The many dynamic flares, CMEs and rolling, boiling of the Sun cause it to vibrate. With very accurate telescopes the vibrations can be measured, and then carefully analyzed to determine properties of the interior. This is a very exciting new field.