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 4pR^{2}x1370 J is passing out from the Sun
every second.

Now the radius of the Earth's orbit is 1.5x10^{11} m and so the energy
emitted by the Sun every second is:

E = 4p1.5x10^{11})^{2}
x1370 = 3.87x10^{26} J.

Using Einstein's mass-energy equation (E =
mc^{2}) you can calculate the mass of the Sun being converted into energy every
second.

Mass converted to energy = E/c^{2}

=
3.87x10^{26}/9x10^{16} = 4.3x10^{9} kg =
4.3x10^{6} tonnes.

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