The Sun contains more than 99.8% of the total mass of the Solar System. Diameter: Mass: Temperature: 1,390,000 km. 1.989e30 kg 5800 K (surface); 15,600,000 K (core)

Astronomy

The Sun is a small star and the central body of our solar system around which the planets revolve and from which they receive light and heat. It is much closer than any of the other stars, and without its exact placement in relation to the Earth, our planet would not be able to support life, or at least life as we know it. The Sun is largely responsible for our weather, powering the winds and evaporating water to form the clouds that bring rain. Currently, the world-wide concern of the scientific community is being directed at the problem of global warming. This is because even slight changes in temperature caused by our human activity can cause catastrophic changes in the delicate balance between the Sun's influence and our climate. And if the Sun itself were to warm or cool even slightly, this too would probably have significant repercussions for our climate.

The Sun has been shining for 5,000 million years. It rotates unevenly, with its period of surface rotation being about 26 days at its equator, but near the poles it can be as much as one rotation every 36 days. This is due to the fact that the Sun is gaseous, rather than a solid body like the Earth. Similar rotational effects to those of the Sun are seen in the gaseous planets. The differential rotation extends considerably into the interior of the Sun, but the core of the Sun rotates in the same way as a solid body, like the Earth. Although it appears as if the Sun is on fire, in fact it is not burning like wood or coal in a fireplace. Rather, it is producing energy like a giant nuclear fusion bomb. In the super-hot core of the Sun, 600 million tonnes of hydrogen atoms smash together every second, turning them into heavier helium atoms. The energy released by this phenomenon escapes into space as life-giving light and heat.

There is a luminous envelope of gas surrounding the Sun. This is called the photosphere. The surface maintains a temperature of about 5800 degrees Centigrade, and this goes as high as 6000 degrees C. Sunspots, which appear periodically on the surface of the Sun, are dark by comparison with the surrounding regions. Sunspots are caused by interactions within the Sun's magnetic field and they have an effect on terrestrial magnetism and other terrestrial phenomena. They are relatively "cool" regions, only 3800 degrees, and can be huge, measuring up to 50,000 km in diameter. Within the dark or 'cool' regions, strong magnetic fields cool the Sun's gases, and the trapped gas appears dark compared to the surrounding brilliance. The appearance of the sunspots is spasmodic, but they increase in number approximately every eleven years, a phenomenon known as the Sun-spot cycle. A very low period of sunspot activity known as the Maunder Minimum, was recorded in the latter half of the 17th century. This coincided with an abnormally cold period in northern Europe sometimes known as the Little Ice Age, although to date, science has not been able to establish any conclusive connection between the two events.

When compared to our terrestrial standards, the Sun's magnetic field is immense, and certainly far more complex. This magnetic field is known as its magnetosphere (sometimes called the heliosphere) and it extends well beyond Pluto. In addition to heat and light, the Sun also emits a low-density stream of charged particles consisting of ionized atoms (especially hydrogen) or electrons. This stream, which is generated throughout the solar system at about 450km per second, is known as the solar wind. The solar wind, and the much higher energy particles ejected by solar flares, can have dramatic effects on the Earth. Among the most spectacular effects is the display of moving streamers or bands. These can appear as 'curtains' of light, and they are caused by the streams of charged particles from the Sun that pass into the Earth's magnetic field. They are better known as the Aurora borealis in the northern hemisphere and the Aurora Australis in the southern hemisphere, and are visible in the higher latitudes. Other effects include power line surges and radio interference. The solar wind also exerts an influence on the tails of comets and has been shown to have a measurable effect on the trajectories of spacecraft.

If you would like to know more about the solar system, Starscine suggests the following websites:

www.nineplanets.org
www.nasa.gov