How much mass does the Sun lose over its lifetime? (Thanks to Dan Fehlauer, Dexter Southfield HS, for suggesting the question.)

China is planning to launch an artificial moon to help illuminate a city at night. How big a satellite would be needed to provide as much illumination as a full moon?

Look for the answers online at

Question suggestions are always welcome!

For more Fermi questions and answers, see Guesstimation 2.0: Solving Today’s Problems on the Back of a Napkin, by Lawrence Weinstein (Princeton University Press, 2012).

AAPT members receive access to The Physics Teacher and the American Journal of Physics as a member benefit. To learn more about this member benefit and becoming an AAPT member, visit the Joining AAPT page.