The different layers of the Sun have different temperatures. For example, the surface of the Sun, the photosphere where the light comes from, is the coolest: 6000 degrees Kelvin, about 10,000 F. The core is about 27 million degrees Fahrenheit. Because we cannot go there with thermometer, this was derived from mathematical models.
For a picture and description, see the webpage
http://fusedweb.pppl.gov/...asmas/SunLayers.html

Mandy

Although we can't directly measure the temperature of the Sun's atmosphere (e.g. with a thermometer), we can measure the temperature based on the type of light that comes from the corona using spectroscopy. This measures the amount of any given ion (an atom with some electrons stripped off) there is in the corona. We know how much energy, and therefore how much heat is used to strip these electrons off an atom and so, we can tell how hot the corona is! The average temperature of the corona is 1 million degrees (Kelvin) but during a solar flare we measure temperatures up to 20 or 30 million degrees! This was very surprising at first and people assumed it was emission from a new element, called Coronium (http://en.wikipedia.org/wiki/Coronium). It wasn't until years later that it was realized this "new" element was actually a form of Iron with 13 electrons stripped off! Claire