SUN: Ultimate Source Of Earth's Energy 

10 Need-to-Know Things About the Sun:

1. The sun is a star. A star does not have a solid surface, but is a ball of gas (92.1 percent hydrogen (H₂) and 7.8 percent helium (He)) held together by its own gravity.

   Earth compared to the sun.

2. The sun is the center of our solar system and makes up 99.8% of the mass of the entire solar system.
3. If the sun were as tall as a typical front door, Earth would be about the size of a nickel.
4. Since the sun is not a solid body, different parts of the sun rotate at different rates. At the equator, the sun spins once about every 25 days, but at its poles the sun rotates once on its axis every 36 Earth days.
5. The solar atmosphere (a thin layer of gases) is where we see features such as sunspots and solar flares on the sun.
6. The sun is orbited by eight planets, at least five dwarf planets, tens of thousands of asteroids, and hundreds of thousands to three trillion comets and icy bodies.
7. The sun does not have any rings.
8. Spacecraft are constantly increasing our understanding of the sun -- from Genesis (which collected samples of the solar wind and returned the particles to Earth) to SOHO, STEREO, THEMIS, and many more, which are examining the sun's features, its interior and how it interacts with our planet. .
9. Without the sun's intense energy there would be no life on Earth.
10. The temperature at the sun's core is about 15 million degrees Celsius (27 million degrees Fahrenheit).

BASIC GOVERNING PHYSICAL PROPERTY OF ALL STARS

The lifecycle of a star is based entirely on its mass and the law of Gravity that operates on that value. Since gravity works to force all mass toward a center, its is concluded that within a mass of a star, the center of mass is the center of the star, and the place where that mass is condensed to the smallest possible space. Unusual properties of Physics govern the form of material in a stellar core, and we will look into those unusual properties later. For now, the simplest rule is that where gravitational pressure is greatest and thus the packing of material the most dense, the temperature will be the greatest. A star with much mass will have a greater gravitational force operating on its mass, generating greater internal pressures and thus higher temperatures. Higher temperatures means greater kinetic energy of the molecules and increased collision frequency, resulting in a greater release of energy. A star with less mass will have less gravitational force operating on it, resulting in lower internal pressures and lower temperatures. The low mass star will have interior particles at lower energy levels, reducing collision frequency and yielding a lower release of energy. To put it more simply, high mass stars burn hot and energetically, and low mass stars burn cool and less energetically. It may seem that high mass stars ought to live longer owing to their greater amount of material, but it is the low mass stars that live longest because they burn what little material they have more slowly.

Our Sun is an average star, and of spectral class G2V. No one on Earth can life long enough to watch the entire lifecycle of our Sun, so we turn to the stars in space to see those of similar mass and at different stages of their lifecycle to make a theoretical picture of what our Sun's life may have been like and will be. We turn to the HR Diagram for this help.

The Sun's power (about 386 billion billion mega Watts) is produced by nuclear fusion reactions. Each second about 700,000,000 tons of hydrogen are converted to about 695,000,000 tons of helium and 5,000,000 tons (=3.86e33 ergs) of energy in the form of gamma rays. As it travels out toward the surface, the energy is continuously absorbed and re-emitted at lower and lower temperatures so that by the time it reaches the surface, it is primarily visible light. For the last 20% of the way to the surface the energy is carried more by convection than by radiation.

The surface of the Sun, called the photosphere, is at a temperature of about 5800 K. Sunspots are "cool" regions, only 3800 K (they look dark only by comparison with the surrounding regions). Sunspots can be very large, as much as 50,000 km in diameter. Sunspots are caused by complicated and not very well understood interactions with the Sun's magnetic field.

A small region known as the chromosphere lies above the photosphere.

The highly rarefied region above the chromosphere, called the corona, extends millions of kilometers into space but is visible only during a total solar eclipse (left). Temperatures in the corona are over 1,000,000 K.

It just happens that the Moon and the Sun appear the same size in the sky as viewed from the Earth. And since the Moon orbits the Earth in approximately the same plane as the Earth's orbit around the Sun sometimes the Moon comes directly between the Earth and the Sun. This is called a solar eclipse; if the alignment is slighly imperfect then the Moon covers only part of the Sun's disk and the event is called a partial eclipse. When it lines up perfectly the entire solar disk is blocked and it is called a total eclipse of the Sun. Partial eclipses are visible over a wide area of the Earth but the region from which a total eclipse is visible, called the path of totality, is very narrow, just a few kilometers (though it is usually thousands of kilometers long). Eclipses of the Sun happen once or twice a year. If you stay home, you're likely to see a partial eclipse several times per decade. But since the path of totality is so small it is very unlikely that it will cross you home. So people often travel half way around the world just to see a total solar eclipse. To stand in the shadow of the Moon is an awesome experience. For a few precious minutes it gets dark in the middle of the day. The stars come out. The animals and birds think it's time to sleep. And you can see the solar corona. It is well worth a major journey.

It just happens that the Moon and the Sun appear the same size in the sky as viewed from the Earth. And since the Moon orbits the Earth in approximately the same plane as the Earth's orbit around the Sun sometimes the Moon comes directly between the Earth and the Sun. This is called a solar eclipse; if the alignment is slighly imperfect then the Moon covers only part of the Sun's disk and the event is called a partial eclipse. When it lines up perfectly the entire solar disk is blocked and it is called a total eclipse of the Sun. Partial eclipses are visible over a wide area of the Earth but the region from which a total eclipse is visible, called the path of totality, is very narrow, just a few kilometers (though it is usually thousands of kilometers long). Eclipses of the Sun happen once or twice a year. If you stay home, you're likely to see a partial eclipse several times per decade. But since the path of totality is so small it is very unlikely that it will cross you home. So people often travel half way around the world just to see a total solar eclipse. To stand in the shadow of the Moon is an awesome experience. For a few precious minutes it gets dark in the middle of the day. The stars come out. The animals and birds think it's time to sleep. And you can see the solar corona. It is well worth a major journey.

The Sun's magnetic field is very strong (by terrestrial standards) and very complicated. Its magnetosphere (also known as the heliosphere) extends well beyond Pluto.

In addition to heat and light, the Sun also emits a low density stream of charged particles (mostly electrons and protons) known as the solar wind which propagates throughout the solar system at about 450 km/sec. The solar wind and the much higher energy particles ejected by solar flares can have dramatic effects on the Earth ranging from power line surges to radio interference to the beautiful aurora borealis.

Recent data from the spacecraft Ulysses show that during the minimum of the solar cycle the solar wind emanating from the polar regions flows at nearly double the rate, 750 kilometers per second, than it does at lower latitudes. The composition of the solar wind also appears to differ in the polar regions. During the solar maximum, however, the solar wind moves at an intermediate speed.

The Sun is about 4.5 billion years old. Since its birth it has used up about half of the hydrogen in its core. It will continue to radiate "peacefully" for another 5 billion years or so (although its luminosity will approximately double in that time). But eventually it will run out of hydrogen fuel. It will then be forced into radical changes which, though commonplace by stellar standards, will result in the total destruction of the Earth (and probably the creation of a planetary nebula).

Shailesh kr shukla

directoratace@gmail.com