It is often said that the Sun is an "ordinary" star. That's true in the sense that there are
many others similar to it. But there are many more smaller stars than larger ones; the
Sun is in the top 10% by mass. The median size of stars in our galaxy is probably less
than half the mass of the Sun.
The Sun is personified in many mythologies: the Greeks
called itHelios and the Romans called it Sol.
The Sun is, at present, about 70% hydrogen and 28% helium by mass everything else
("metals") amounts to less than 2%. This changes slowly over time as the Sun converts
hydrogen to helium in its core.
The outer layers of the Sun exhibit differential rotation: at the equator the surface
rotates once every 25.4 days; near the poles it's as much as 36 days. This odd behavior
is due to the fact that the Sun is not a solid body like the Earth. Similar effects are seen
in the gas planets. The differential rotation extends considerably down into the interior of
the Sun but the core of the Sun rotates as a solid body.
Conditions at the Sun's core (approximately the inner 25% of its radius) are extreme.
The temperature is 15.6 million Kelvin and the pressure is 250 billion atmospheres. At
the center of the core the Sun's density is more than 150 times that of water.