Saramsha

No. 045  ·  31 October 2026

Fifty Minutes Later

Each day the Moon rises about fifty minutes later than the day before — a drift large enough that, once a month, some calendar day gets no moonrise at all, and another gets two. Pick a place and a date and watch your own month of moonrises.

Offsets are standard-time estimates — this page doesn't know about daylight saving, so nudge the offset yourself if your clock has shifted.

moonrise   no moonrise that day   two moonrises that day

About this piece

A day late, fifty minutes at a time

The Earth turns once relative to the Sun in 24 hours — that is what a day is. But the Moon is not fixed against the stars; it slides eastward along its orbit by about 13.2° every day, roughly its own width every hour. For the Moon to clear the eastern horizon again, the Earth has to turn a little further each time to catch up with it, and that little further costs about fifty minutes. A solar day is 24h00m; the time between one moonrise and the next averages about 24h50m. That 50-minute gap, not any irregularity, is the whole mechanism.

Fifty minutes a day, repeated, adds up to a full 24 hours in just under a month — 1440 ÷ 50 ≈ 29 days, which is suspiciously close to the 29.53-day synodic month, because it is the same fact seen twice: a "lunar day" (one moonrise to the next) and a full cycle of phases both come from the same slow eastward drift against the Sun. Somewhere in that month, the 50-minute delays push a moonrise past midnight into the next calendar date, and whichever date gets stepped over has no moonrise at all. The date before it, or occasionally the date after, picks up the overflow and gets two. Nothing is skipped physically — the Moon rises on schedule, every 24h50m, without fail. It is only the calendar's 24-hour boxes that sometimes miss one.

What is actually computed here

For the chosen place, this page works out the Moon's position in the sky — its right ascension and declination — at ten-minute steps using the standard short-period lunar position terms (the ones accurate to a few arcminutes, not the full few-hundred-term theory an almanac uses). It combines that with the place's latitude, longitude and your chosen UTC offset to get the Moon's altitude above the horizon at each step, correcting the horizon for the Moon's parallax the way professional almanacs do, then finds the exact minute each rise or set crosses zero by straight-line interpolation between steps. The same lunar position also gives the Sun–Moon angle used for the illuminated fraction shown as the phase icon. Expect results within a minute or two of an observatory almanac — plenty for planning, not enough to time an eclipse.

The phase icon assumes a Northern-Hemisphere sky, where the lit edge grows on the right as the Moon waxes. South of the equator the same Moon looks mirrored — lit on the left while waxing — because you are looking at it upside down relative to a northern observer.