By the Light of the Moon?
A sundial can be used as a moondial one week before and after the time the full moon. This is the only time a moondial will work because the moonlight has to be bright enough to cast a shadow on a sundial. If we make the right corrections, we can use the sundial to tell the time at night.
| Days from Full Moon | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 |
| Amount of Correction | 0:00 | 0:48 | 1:36 | 2:24 | 3:12 | 4:00 | 4:48 | 5:36 |
We can use this table to make the proper corrections. The days before the full moon the time shown by the moonlight is "fast" (subtract the time on the table), and the days after the full moon the time shown by the moonlight is "slow" (add the time on the table).
For example, if the time read by the moondial says 11:00 and it is three days after the full moon, we simply add 11:00 + 2:24 = 1:24 a.m. Remember this time is just a rough approximation.