The skipped moonrise: a 50-minute daily lag, blank tide tables, two-week polar nights
Have you ever looked at a printed calendar and found a day that's just blank — a day where the moon, uh, just doesn't bother to rise at all? Hey, I'm Salt. I'm Grace. Okay, wait. A day with no moonrise?
It happens more than you'd think. Our 24-hour clock doesn't quite line up with the solar system. The Earth is spinning, but the Moon is also orbiting us in that same direction, so by the time Earth does one full rotation and you're standing back where you started, the Moon has moved ahead a bit on its own track. So we just have to spin a little further to see it again. Right.
The math from Astronomy Cafe lays this out really clearly. It takes us on average an extra 50 minutes to catch up. So the time between consecutive moonrises is actually 24 hours and 50 minutes. Which means the moon is 50 minutes late every single day. Pretty much.
And that daily drift adds up. Say the moon rises at 11:50 PM on a Sunday. The next moonrise happens 24 hours and 50 minutes later. So, Grace, that puts you at 12:40 AM on Tuesday. You just skipped Monday.
You're kidding. Monday gets no moonrise. It gets a moonset, sure, but no rise. It just slips right past midnight. I feel like I'd notice a blank day on my wall calendar.
A lot of modern calendars just smooth it over or use an approximation. But traditional calendars track it rigorously, because it it — it really matters. The ancient Hawaiians documented these blank days in their agricultural tracking, as detailed in the Ulukau archives. They used the precise lunar phases for planting and for cultural taboos. If your planting schedule is based on the moon, a missing day probably throws everything off.
Exactly. And traditional Hindu astronomical calendars — the Panchangs — they build their system around these missing days. There was one just last week, on August 12, 2026. Okay, that's new. Yeah.
The Hindustan Times covered it. It fell during Krishna Amavasya, the new moon phase. Because their agricultural cycles and religious fasts are tied to the exact lunar positions, a day without a moonrise alters how the ceremonies are timed. That makes sense. If your fasting window opens when the moon comes up, you know, you need to know if it's actually going to show up that day.
Right. And Salt, hunters track this stuff too. A guy named John Alden Knight looked into this back in 1926. What was he trying to figure out? Fish feeding patterns, mostly.
He compiled data across 39 different U. S. cities, building what he called Solunar Theory. He found that because of this 50-minute lag, about 3. 6 percent of days throughout the year lack a moonrise entirely.
Three point six percent. That's, what, like twelve or thirteen days a year? Roughly. He used those blank days to predict peak wildlife activity. The premise was that animal behavior is anchored to the 24-hour-50-minute tidal day, not our human midnight, so you have to track the the — the exact moonrise drift to know when the fish will bite.
Does this happen everywhere? Like, if I'm standing on the equator, am I missing thirteen days a year? You are, but it's very predictable down there. Equatorial observers experience a missing moonrise on a strict 29-day cycle. You just wait a month and it happens again.
But if you move north or south, the geometry gets really weird. How weird? Well, according to Astronomy magazine, once you cross 66. 5 degrees north or south — up near the Arctic or down in Antarctica — the angle of the moon's orbit means it can just stay above the horizon. Or below it.
Hold on. It doesn't rise or set. Because the Earth is tilted, and the moon's orbit is tilted on top of that, an observer near the pole — if you're standing up there, you can watch the moon just circle the sky for days. It stays up there, or it stays hidden beneath the ice, for up to two straight weeks without a single moonrise. That can't be right.
I know. The geometry sort of breaks down. There's this great thread on a Stack Exchange forum where someone is trying to map the tidal day, and they realize that at high latitudes you just get a fortnight of continuous moonlight followed by a fortnight of dark. So the whole concept of a daily rise and set vanishes. So up there, the 50-minute delay is just irrelevant.
You aren't skipping a Monday, you're skipping half the month. Yeah, it throws the daily math out the window. Which brings us back to the printed charts. NOAA puts out these highly detailed tide tables for mariners every year. And the analysts there...
well, they just have to print the blanks. Because there's literally no time to put in the box. Right. If you thumb through a NOAA tide book, you'll find asterisks printed right there in the columns where a time should be. The next time you spot a blank entry or an asterisk in a local tide chart, you'll know you're looking at the exact boundary where our artificial twenty-four hour clock fails to keep pace with the cosmic rhythms of the solar system.
Thanks so much for listening.
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