This unit of measure is convenient because a supernova typically releases about one foe of observable energy in a very short period (which can be measured in seconds). In comparison, if the Sun 's current luminosity is the same as its average luminosity over its lifetime, it would release 3.827 × 10 W × 3.1536 × 10 s / yr × 10 yr ≈ 1.2 foe. One solar mass has a rest mass energy of 1787 foe.