Hot objects emit light (glow). You know this from hot metal on a stove or coals in a fire: this is why they glow. The hotter something is, the shorter the wavelength of the light that it will emit. What we see as color is in fact wavelength, so we can easily measure the wavelength, and therefore, the temperature of a hot glowing object. The color of the sun's glow is yellow-green, and the temperature that of something that glows that color is about 5,200 degrees C. Therefore, the surface of the sun is about 5,200 degrees C.

The surface of the Sun is about 5505 degrees Celsius on average.We know this because of the spectrum of light it produces. Have you noticed how you can tell whether something is hot based on its color? We talk about "red hot" when something is hot enough to glow red. That's usually about 500-800 degrees C. If we keep increasing the temperature, it starts to look more of a yellow-white, then bright white, and eventually blue-white, although it would be too bright to look at. We can measure the temperature of objects on Earth that have the same spectrum of colors as the Sun has. In fact, there is an equation called Planck's Law which calculates how bright each color will be for a given temperature.

Youre right- the sun is way too hot to get close enough to measure the temperature using a thermometer, which is probably how youre accustomed to finding the temperature of things! The exact way scientists found the temperature of the sun involves a lot of really complicated physics equations, but I can tell you that they calculated the temperature by looking at the light (energy) that comes from the sun. You will be able to investigate this in more detail as you get older and learn more math!