The Sun is the star at the center of the Solar System. The Sun has a diameter of about 1,392,000 kilometers and by itself accounts for about 99.86% of the Solar System's mass; the remainder consists of the planets (including Earth), asteroids, meteoroids, comets, and dust in orbit. About three-quarters of the Sun's mass consists of hydrogen, while most of the rest is helium. Less than 2% consists of other elements, including iron, oxygen, carbon, neon, and others.
The mean distance of the Sun from the Earth is approximately 149.6 million kilometers, though this varies as the Earth moves from perihelion in January to aphelion in July. At this average distance, light travels from the Sun to Earth in about 8 minutes and 19 seconds. The energy of this sunlight supports almost all life on Earth by photosynthesis,and drives Earth's climate and weather. An accurate scientific understanding of the Sun developed slowly, and as recently as the 19th century prominent scientists had little knowledge of the Sun's physical composition and source of energy. This understanding is still developing.
Source: en.wikipedia.org/wiki/Sun - 25.03.2010
The sun - our most important source for heat and light and its counterpart the moon, lightning the night with its gentle glow without bothering it, completed with the sumless stars. For us they are well-tried facilities in time and space.