Solar energy

The amount of energy emitted from the Sun can be found using the value of the solar constant.
From this the rate at which the Sun is converting mass into energy can also be calculated.

If we take the solar constant to be 1370 Wm^-2 at a distance equal to the radius (R) of the Earth's orbit. This means that a total amount of energy equal to 4πR²x1370 J is passing out from the Sun every second.

Now the radius of the Earth's orbit is 1.5x10¹¹ m and so the energy emitted by the Sun every second is:
E = 4π1.5x10¹¹)² x1370 = 3.87x10²⁶ J.

Using Einstein's mass-energy equation (E = mc²) you can calculate the mass of the Sun being converted into energy every second.

Mass converted to energy = E/c²
= 3.87x10²⁶/9x10¹⁶ = 4.3x10⁹ kg = 4.3x10⁶ tonnes.

This means that the Sun is converting over four million tonnes of its mass into energy every second!