The Sun

[GrahamT]

How does the sun function?  What are it's physical properties and what sustains it?

[bernardo]

The pressure in the middle is so high that the atoms get squashed and set off a nuclear reaction.  It's burning itself up at the rate of 4 million tonnes per second.

[QmunkE]

In the sun's core, hydrogen nuclei (actually deuterium) undergo nuclear fusion (the same process that occurs in hydrogen bombs). This fusion creates a helium nucleus and releases vast amounts of energy in the form of photons.

Eventually, all the hydrogen will be used up, the core will begin to collapse until the pressure and heat are great enough for the sun to begin to fuse the helium into larger elements. The star's outer layers will begin to swell, expanding greatly into the solar system, engulfing Mercury, Venus and Earth.

But don't worry, it won't happen for about 4.5 - 5 billion years yet!

(data from the Melbourne Planetarium)
Average Distance from the Earth:
149.6 million km (1.0 AU)
Size (Equatorial Diameter):
1 392 000 km (109 x that of Earth)
Mass:
1.989 x 1030 kg (333 000 x that of Earth)
Rotation Period:
27.28 days (Synodic Period)
25.38 days (Sidereal Period)
Temperature:
5 500�C (surface)
15 000 000�C (core)