Are full moon days warmer?
No difference
"Full-moon nights are frosty" — and also "full moons are warm": farmers and mountaineers pass down both. And studies really have reported full-moon days a tiny fraction warmer, so this one deserves a careful look.
Los Angeles
- Average (whole period)
- 17.6°C
- Full moon days (±24h)
- +0.05°C vs monthly mean
- New moon days (±24h)
- +0.07°C vs monthly mean
- Verdict for full moon days
- No difference
Tokyo
- Average (whole period)
- 14.4°C
- Full moon days (±24h)
- −0.06°C vs monthly mean
- New moon days (±24h)
- −0.03°C vs monthly mean
- Verdict for full moon days
- No difference
Berlin
- Average (whole period)
- 9.3°C
- Full moon days (±24h)
- −0.08°C vs monthly mean
- New moon days (±24h)
- −0.08°C vs monthly mean
- Verdict for full moon days
- No difference
Data: 1940–2025, ERA5 reanalysis (daily mean temperature)
Act II: If not the moon, what moves the thermometer?
Came looking for a difference? Here is a real one.
+13.0°C
In Los Angeles, the warmest month (August) and the coldest (January) sit 13.0°C apart. The seasons routinely move hundreds of times what the moon is even accused of (±0.1°C-ish).
Comparing the first decade on record with the latest: +1.2°C on average (the hottest daily mean on record: 34.8°C on June 27, 1990). The suspect list for that trend includes the heat that pavement and buildings store up, ever-accumulating greenhouse gases, and slow multi-decade swings of the oceans. The only name missing from the list is the moon — a suspect on a 29.5-day cycle cannot produce a decades-long one-way drift.
Whether tonight runs hot or cold, ask the season and the weather map — not the moon's age.
"Full-moon nights are frosty" — and also "full moons are warm"
Temperature folklore about the moon is delightfully contradictory. Farmers and mountaineers will tell you full-moon nights are clear and cold, frost-prone from radiative cooling; other traditions insist frost won't settle under a full moon. People who spend nights outdoors earned those instincts the hard way, and we won't laugh them off from an armchair. Instead, this page tests them on their own turf — decades of measured temperatures.
A real study did find full moons slightly warmer
This one is not pure occultism. In 1995, Balling & Cerveny reported from satellite data that the lower atmosphere runs a tiny fraction warmer around full moons — about two hundredths of a degree. Candidate mechanisms include the atmospheric tide raised by lunar gravity and the full moon's reflected and infrared radiation. The key number is the size: 0.02°C. No household thermometer can measure it and no human will ever feel it. The question for this page is not "is the effect exactly zero" but "is it big enough to matter to anyone."
How the verdict is computed
- Temperatures are ERA5 reanalysis daily means (via Open-Meteo) for Los Angeles, Berlin, and Tokyo — three cities on three continents, so the answer doesn't hinge on one lucky location (since 1940)
- Temperature crosses 0°C, so the ratio scale (normal = 1.00) used by our other topics doesn't work here. Instead we compare deviations (°C) from the same-month average
- For full-moon days (within ±24h of the instant, judged at each city's noon) and new-moon days, the mean deviation is evaluated with a 95% confidence interval; under ±0.3°C displays as "practically none," above ±1.0°C as "warmer/cooler"
- Monthly averages absorb the warming trend; full-moon days are spread uniformly across the decades, so the trend cancels out of the comparison
See the methodology for the verdict thresholds.
About "full moons mean clear, cold nights"
The radiative-cooling story hides a classic reversal of cause and effect. It isn't that full moons clear the sky — it's that a clear sky is what lets you see the full moon. Cloudy full moons leave no memory. A brilliantly clear, cold night with a full moon overhead is textbook confirmation bias. And as our rain topic confirmed, precipitation shows no sign of caring about the moon either.
Sources
- Open-Meteo Historical Weather API (ERA5 reanalysis, CC-BY 4.0)
- Balling RC, Cerveny RS. "Influence of lunar phase on daily global temperatures" Science 1995;267:1481-1483
- Lunar phases computed in-house from Jean Meeus, "Astronomical Algorithms" (UTC)
Last updated: June 13, 2026 03:21 UTC (rebuilt daily)