# 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 4

pR

^{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 = 4

p1.5x10

^{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!