Great question! The sun is really hot: about 10 million degrees Celsius, but it is not the hottest star in the Universe! Some stars reach temperatures of 3 billion degrees. That’s 300 times hotter than the sun!

The sun is actually "average" in terms of how hot and how big it is! There are many starts (blue and white stars, for instance) that burn hotter than the sun.

The hottest stars are blue giants. For example, Eta Carinae is about 180 times the size (diameter) of our sun, and has a surface temperature of 40 000 degrees Celcius (72 000 F).

(Our sun looks white from space, and has a surface temperature of 6000 C (10 000 F). More recently, in 2005 a star at the center of the Red Spider Nebula was found to have a temperature of 300 000 C (540,000 F). It's so hot that it doesn't glow blue, it actually glows X-ray...

(X-ray isn't a color, obviously, but the energy of the emitted light is so high that it's invisible, and largely in the same energy as X-rays)

No, the sun has a pretty average temperature for a star: there are much hotter stars, and there are much cooler stars as well.

Did you know that the color of a star is related to its temperature? If a star looks red, that means its surface temperature is approximately 2,500 Kelvin (where Kelvin is another system to talk about temperature like Fahrenheit or Celcius). Our Sun, which is a white star, is about 6,000 Kelvin. That´s hot, right! But the hottest stars are the blue stars. When a star gets above 10,000 Kelvin it´s surface appears blue to our eyes. And the hottest stars are the very big blue stars, which we call blue hypergiants. These stars are more than 100 times larger than the Sun. On example of one of these very big, very hot stars is the star Eta Carinae which is about 7,500 light years away from the Sun. Eta Carinae is more than 180 times larger the Sun and its surface temperature is around 40,000 Kelvin. That´s 72,000 degrees Fahrenheit (and for comparison, your body temperature is 98.6 degrees Fahrenheit... so 72,000 is very very hot!!