The sun shines every day and we don't really think about it. But the amount of energy that the sun produces is astounding.
How much energy is the sun producing? On earth we see about 1 kilowatt per square meter of sunshine. In space (because there is no atmosphere) it is more like 2 kilowatts per square meter. The sun is about 150 million kilometers from earth. Since the sun is spraying 2 kilowatts per square meter in all directions, we can calculate the surface area of a sphere with a radius of 150 million kilometers:
4 * pi * (150 million kilometers)^2 = 283,000,000,000,000,000 square kilometers.
Multiply that by a million to get square meters. So the sun is producing something like:
(This page says 3.8 x 10^26 watts, which is close enough)
To produce all that energy, the sun uses nuclear fusion. Nuclear fusion turns mass into energy. So... How much mass does the sun convert per second to produce all that energy? Here's the answer:
The answer? "The Sun is using losing 4 billion kilograms of mass a second." If it is losing that much mass every second, why hasn't the sun disappeared? See the article for the answer, which is even more amazing.