IAO 1998, Теория, 14–16 години — Задача 5

The Moon diameter is $3476\,\mathrm{km}$, and the visible angular diameter of the lunar disk is $31'$. Therefore, the maximum visible diameter of the Mare Crisium is

This is 3–5 times more than the angular resolution limit of a naked eye. Indeed, good observers can see the Mare Crisium, that was proofed by the pretelescopic draws of the Moon.