Although in all respects an ordinary and unexceptional star, the Sun – because it is so much nearer to us than any other star – is the only star whose features and characteristics can be studied in depth and detail.

Located at a mean distance of 149,600,000 km – 1 AU – the Sun is an incandescent gaseous body with a radius of 696,000 km (109 times that of the Earth). Although its huge globe could contain about 1.3 million bodies the size of our planet, the Sun has a mass only about 330,000 Earth masses, and its mean density, therefore, is only about one quarter that of the Earth – about 1,400 kg/m3. This relatively low density, together with spectroscopic evidence, indicates that the Sun is composed predominantly of the lightest chemical elements. Its composition, by mass, is about 73.5 percent hydrogen, 25 percent helium, and about 1.5 percent heavier elements, with the most abundant of the heavier elements being carbon, oxygen, nitrogen, neon, and iron.

The Sun's effective surface temperature is about 5800 K and its luminosity – the total amount of energy radiated into space every second – is 3.86 × 1026 watts. Because solar radiation spreads out isotropically (equally in all directions), the solar flux – the amount of radiant energy per second passing perpendicularly through an area of 1 square meter – decreases with the square of distance.