How much mass does the Sun lose over its lifetime? (Thanks to Dan Fehlauer, Dexter Southfield HS, for suggesting the question.)
Answer: To estimate this, we need to estimate the lifetime of the Sun and its power output. The solar system is about 5 billion years old. We can estimate that the Sun’s total lifetime is between 1 and 10 times its existing age, giving a lifetime of 2×1010 years. We can estimate the Sun’s power output in a few ways. If we remember the Stefan-Boltzmann equation, we can use the surface temperature of the Sun and its radius to calculate the power output. If we remember from reading Guesstimation that the Sun’s power density is 10−4 of a human, we can use its mass to calculate its power output. However, the most useful number (for this and other purposes) is the solar flux at Earth orbit, which...
