Do home runs rise on full-moon nights?
No difference
These are home-run totals (both teams) for every Major League game. Because the folklore is about the full-moon night, we split night games from day games.
Night games
- Average (whole period)
- 1.84 per game
- Full moon days (±24h)
- 1.85 per game
- New moon days (±24h)
- 1.85 per game
- Verdict for full moon days
- No difference
- Data
- 1935–2025, 179,041 HR
Day games
- Average (whole period)
- 1.30 per game
- Full moon days (±24h)
- 1.30 per game
- New moon days (±24h)
- 1.28 per game
- Verdict for full moon days
- No difference
- Data
- 1901–2025, 150,004 HR
Act II: What clearly moved home runs
Here is the difference this data does show clearly.
×5.2
Home runs per game peaked at 2.82 in 2019 and sank to 0.54 in 1944. What clearly drove the long ball was the era and the ball — some years it carries, some years it doesn't.
The wildest day for home runs was July 2, 2002 — 62 of them across 15 games. What did it was that day's hitting and ballparks.
In this data at least, the ball, the parks and the summer heat moved home runs far more than anything else. We're still looking for the moon's part.
The folklore that the ball flies on full-moon nights
Ballparks have long carried the saying that home runs come out under a full moon. A full moon stirs the batter up; a bright night makes hitters swing for the fences — it's the same family as the folklore about crime and accidents. And the heart of moon folklore is always the full-moon night. If that were true, the effect should show up in night games, when the moon is actually in the sky, not in day games. So do home runs really rise on full-moon days? This page checks it every day across every Major League game.
How this verdict is calculated
- The data is home-run totals (both teams) for every Major League Baseball (MLB) game. We split games into night games and day games — because the folklore is about the night, that's where any effect should appear
- Home runs per game vary enormously by era (almost none in the dead-ball years, soaring in the recent "juiced ball" seasons). So we use the home runs per game for the same year and month as the expected baseline, and compare the observed-to-expected index
- Using the moon's age at noon (US Eastern) on each game day, we mark full-moon days (within ±24h of the exact moment) and new-moon days, and compare each group's average index against normal (1.00)
See the methodology for the full criteria.
Reading the data
- Home-run totals depend heavily on the size of the ballparks, that year's ball, the temperature, and altitude (the ball carries in thin air). This page levels those out by comparing within the same year and month, and looks only at the single question of the full moon
- This page asks one thing: whether home runs per game visibly rise on the calendar's full-moon days
What we can't see yet
This result doesn't mean "the moon has nothing to do with it." Here is what the current method can't see:
- Whether the moon was in the sky: domed stadiums, cloudy nights, and games before moonrise are all counted the same way for now
- Individual players: if some hitters were more affected than others, the league-wide total would dilute it
What we want to check next
- Compare only open-air games played after moonrise
- Line up moonrise times with game times
Perhaps the ballpark saying holds something we haven't yet turned into numbers. We'd like to find it in the data one day.
Data sources
- Retrosheet — Game Logs (date, day/night, and home runs for every game)
- The information used here was obtained free of charge from and is copyrighted by Retrosheet.
- The moon's age and the exact syzygy moments are computed in-house using the algorithms in Jean Meeus, "Astronomical Algorithms" (UTC basis)
Last updated: October 7, 2026 00:48 UTC (rebuilt daily)