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The Sun is mostly made
up of two light gases, 75 per cent hydrogen and 23 per cent helium, with relatively small quantities of other elements - including metals such as gold. Helium was discovered in the Sun before it was detected on Earth. Its name comes from helios, the Greek word for sun.
Temperature
The Sun has a surface temperature of 5,880K but it can be 56,000,000K at its core. (K represents Kelvin, which is an astronomical temperature; it can be converted to Celsius by subtracting 273.16.) At the Sun's centre, nuclear fusion constantly changes hydrogen into helium, and the energy and heat released from this process rise to the surface. The yellow surface we see is called the photosphere.
The corona
The outermost layer of the Sun extends millions of kilometres into space but is visible only during eclipses. At a height of 75,000km in the corona, the temperature may reach 2,000,000K
Rotation
The Sun rotates once every 25.4 days, but because it is not solid like a planet or moon, the poles spin at a different rate, taking as much as 36 days to complete a single revolution.
Solar eclipses
When the Moon lies between the Earth and the Sun, it blocks out the light causing either a partial or total eclipse. At this time, astronomers are able to observe the corona in detail.