Last updated: 2026-04-02

References

1. Science News Explores (2019). Scientists Say: Supermoon. Science News Explores. Link
2. Jet Propulsion Laboratory (n.d.). Measuring the Supermoon. NASA JPL Edu. Link
3. EarthSky Team (2025). Does a supermoon have a super effect on us? EarthSky. Link
4. Thompson, A. (2026). What is a supermoon and when can you see the next one in 2026? Space.com. Link

How Supermoon Cycles Actually Work Over Time

Because the sidereal and synodic months are different lengths, the alignment between full moon and perigee drifts continuously. What many people don’t realize is that supermoons tend to cluster in runs of two or three consecutive months, then disappear for a year or more. This happens because perigee advances roughly 3 degrees per month relative to the lunar phases, completing a full lap in about 8.85 years — a cycle astronomers call the anomalistic year of the lunar orbit.

In practice, this means 2024 produced four full supermoons (August through November), while some years produce only two. NASA’s Jet Propulsion Laboratory publishes lunar perigee tables years in advance, and cross-referencing those with full moon dates shows the pattern clearly. The closest supermoon in recent decades occurred on November 14, 2016, when the Moon reached 356,509 km — the nearest full moon since January 26, 1948. The next comparable approach won’t happen until November 25, 2034, according to JPL ephemeris data.

This long-cycle context matters for calibrating expectations. If you miss the 2034 event, the next comparably close full moon falls in 2052. For anyone genuinely interested in the most dramatic version of the phenomenon rather than a standard supermoon, those peak-of-cycle dates are worth marking on a calendar now. Outside those rare extremes, the difference between one supermoon and the next is typically only a few hundred kilometers — a fraction of a percent of the Moon’s average distance of 384,400 km.

Tidal Effects: Where the Physics Is Unambiguous

While the visual payoff of a supermoon is modest, the gravitational effects are real and measurable. Ocean tides follow an inverse-cube law (not inverse-square), which makes them more sensitive to distance changes than brightness is. When the Moon is at perigee during a full or new moon, tidal forces are approximately 18% stronger than at apogee syzygy, according to NOAA tidal modeling data.

These are called perigean spring tides, and coastal flood managers take them seriously. NOAA’s 2019 technical report on nuisance flooding documented that perigean spring tides contribute to “sunny day” coastal flooding events in low-lying areas — particularly along the U.S. East and Gulf Coasts — with measurable increases in flood frequency during supermoon windows. Specific gauges in Norfolk, Virginia, recorded water levels 1.5 to 2.0 feet above the standard high-tide line during the November 2016 supermoon event.

What supermoons do not do, despite persistent claims, is trigger earthquakes or volcanic eruptions. A 2016 analysis published in Nature Geoscience by Ide, Yabe, and Tanaka found a statistical correlation between large earthquakes (magnitude 8+) and high tidal stress periods, but the effect size was small and the authors explicitly cautioned against predictive use. For events below magnitude 8 — which account for the vast majority of seismic activity — no reliable correlation has been established in peer-reviewed literature.

Photography: What the Numbers Tell You to Actually Do

If you want a photograph that captures the supermoon’s scale, the worst approach is pointing a phone at the sky. A standard smartphone camera has a field of view around 75 degrees; the Moon subtends only about 0.54 degrees at average distance and roughly 0.57 degrees at perigee. That’s less than 1% of the camera’s frame width, producing the small, featureless disk familiar from disappointing supermoon photos.

To fill a frame meaningfully, you need a focal length of at least 500mm on a full-frame equivalent sensor. At 500mm, the Moon occupies roughly 5mm of a 36mm sensor — visible but not dominant. At 1200mm, it fills about 12mm and becomes a genuine subject. Telephoto superzooms in the 800–1200mm equivalent range (such as the Nikon P1000, which reaches 3000mm equivalent) are popular for this reason.

The more effective compositional technique is the lunar alignment shot — photographing the Moon rising or setting behind a distant landmark using a long lens. This leverages the Moon illusion, not the actual size difference. Sites like PhotoPills and The Photographer’s Ephemeris provide alignment calculators that show exactly where and when the Moon will rise behind a specific structure on any given date. During a supermoon, the Moon is also brighter by roughly 0.28 magnitudes compared to an average full moon, which slightly extends the usable shooting window before the sky fully darkens — a practical advantage that’s easy to overlook.

Frequently Asked Questions

How much bigger does a supermoon actually look compared to a regular full moon?

At maximum perigee, the Moon’s angular diameter reaches approximately 33.5 arcminutes versus about 29.4 arcminutes at apogee — a 14% difference in apparent diameter. In practice, without a side-by-side comparison, most observers cannot detect this difference reliably. Studies on the Moon illusion confirm that human angular size perception is poor in featureless sky conditions.

How many supermoons occur in a typical year?

Using Richard Nolle’s original 90%-of-perigee definition, roughly 3 to 4 full moons per year qualify. Some media outlets use stricter thresholds — within 360,000 km, for example — which reduces the count to 1 or 2 per year and makes individual events feel more significant.

Do supermoons cause higher tides than normal spring tides?

Yes. Perigean spring tides — which occur when a new or full moon coincides with perigee — produce tidal forces roughly 18% stronger than apogean spring tides, according to NOAA modeling. Coastal areas already prone to nuisance flooding can see water levels 1 to 2 feet above normal high tide during the closest supermoons.

Who actually coined the term “supermoon” and when?

Astrologer Richard Nolle introduced the term in a 1979 article in Dell Horoscope magazine. It went largely unnoticed until the internet era amplified it. The scientifically preferred term remains perigee syzygy, though that phrase has understandably failed to trend on social media.

When is the next exceptionally close supermoon after 2024?

The next supermoon comparable in distance to the record November 2016 event (356,509 km) is projected for November 25, 2034, based on JPL lunar ephemeris calculations. Standard supermoons occur nearly every year, but that level of proximity happens roughly once per decade due to the 8.85-year anomalistic cycle of the lunar orbit.

References

1. Ide, S., Yabe, S., & Tanaka, Y. Earthquake potential revealed by tidal influence on earthquake size-frequency statistics. Nature Geoscience, 2016. https://doi.org/10.1038/ngeo2796
2. National Oceanic and Atmospheric Administration (NOAA). Nuisance Flooding and the Changing Tidal Flood Paradigm. NOAA Technical Report NOS CO-OPS 086, 2019. https://tidesandcurrents.noaa.gov/publications/techrpt86_PaP_of_nuisance_flooding.pdf
3. Espenak, F. Perigee and Apogee of the Moon: 2001–2100. NASA/GSFC Eclipse Web Site, 2014. https://eclipse.gsfc.nasa.gov/SEhelp/moonperigee.html

Frequently Asked Questions

Last updated: 2026-04-02

References

1. Richter, F. M. (1983). A simple explanation of why Earth’s yearly orbit has an irregular length. Journal of Geophysical Research: Solid Earth. Link
2. US Naval Observatory. (n.d.). Leap Seconds. US Naval Observatory. Link
3. Seidelmann, P. K., & McCarthy, D. D. (2009). The Calendar and the Gregorian Reform. Celestial Mechanics and Dynamical Astronomy. Link
4. Blackburn, B., & Holford-Strevens, L. (1999). The Oxford Companion to the Year. Oxford University Press. Link
5. Dershowitz, N., & Reingold, E. M. (2008). Calendrical Calculations: The Ultimate Edition. Cambridge University Press. Link
6. Espenak, F. (2005). Calendar: The 400-Year Cycle of the Gregorian Calendar. NASA Eclipse Website. Link

How Different Cultures Handled the Switch — and Why Some Never Did

Catholic countries — Spain, Portugal, Poland, and the Italian states — adopted the Gregorian Calendar almost immediately in October 1582. France followed in December of the same year. Protestant and Orthodox nations resisted for decades or centuries, viewing the reform as a papal imposition rather than a scientific correction.

Britain and its American colonies did not switch until 1752, by which point the accumulated Julian drift required dropping 11 days (an extra day had accrued since 1582). The British Calendar Act of 1752 removed September 3 through September 13, producing the famous historical curiosity that George Washington was born on February 11, 1731 under the Julian Calendar but celebrated his birthday on February 22 under the Gregorian system — the same physical day, two different dates.

Russia held out until 1918, after the Bolshevik Revolution, by which point 13 days needed to be skipped. This is why the October Revolution of 1917 is commemorated on November 7 in the modern calendar. The Russian Orthodox Church still uses the Julian Calendar for religious purposes, meaning Christmas falls on January 7 by Gregorian reckoning. Greece was the last European country to fully adopt the Gregorian Calendar, doing so in February 1923. Ethiopia uses its own calendar system with 13 months, placing it roughly 7 to 8 years behind the Gregorian count depending on the time of year.

The International Organization for Standardization codified the Gregorian Calendar as the global civil standard in ISO 8601, first published in 1988, which is why all international business, aviation, and computing timestamps default to this system regardless of local religious calendars.

The Leap Second Problem: An Even More Awkward Correction

Leap years correct for Earth’s orbital period, but a separate problem involves Earth’s rotational speed. The planet’s rotation is gradually slowing due to tidal friction from the Moon — at a rate of approximately 1.4 milliseconds per century per day. This means atomic time, which is perfectly uniform, and astronomical time, which tracks Earth’s actual rotation, continuously drift apart.

Since 1972, the International Earth Rotation and Reference Systems Service (IERS) has inserted 27 leap seconds into Coordinated Universal Time (UTC) to keep the two systems within 0.9 seconds of each other. Leap seconds are added at 23:59:59 on December 31 or June 30, creating a minute that runs 23:59:60 before rolling to 00:00:00.

This creates real engineering problems. In 2012, a leap second insertion caused outages at Reddit, LinkedIn, Mozilla, and Qantas due to software that could not handle a 61-second minute. The Linux kernel and Java both had documented bugs triggered by that single second. In response, the General Conference on Weights and Measures voted in November 2022 to abolish the leap second by 2035, replacing it with a larger, less frequent correction that will be applied no more than once per century. The exact mechanism for that future correction has not yet been finalized, meaning astronomers and software engineers are both watching the same policy discussion for very different reasons.

The contrast with the leap year is instructive: the Gregorian three-part rule runs automatically, requiring no human decision. The leap second requires a deliberate international vote every time it is applied, which is precisely why the engineering community wants it eliminated.

What Happens to People Born on February 29

People born on February 29 — called leaplings or leap-day babies — face a genuine legal and logistical ambiguity in many countries. Approximately 5 million people worldwide share this birthday, based on the roughly 1-in-1,461 probability of being born on a leap day. In any given non-leap year, jurisdictions differ on whether a leapling’s legal birthday falls on February 28 or March 1.

In the United Kingdom and Hong Kong, the legal birthday in non-leap years is March 1. In New Zealand, it is February 28. In the United States, there is no single federal standard — it varies by state statute and context. This matters practically for age-based thresholds: driving licenses, voting eligibility, retirement benefits, and alcohol purchase laws. At least two U.S. court cases have specifically addressed what date a leapling officially “turns 18,” with outcomes depending on state law.

Insurance actuarial tables treat February 29 births identically to February 28 for mortality calculations, according to standard industry practice described in Society of Actuaries documentation. Passport and identification systems handle the date differently across countries: some systems store “0229” as a valid date, while older legacy government databases default to “0228” or “0301,” occasionally causing document mismatches when leaplings travel internationally.

Statistically, the Honor Society of Leap Year Day Babies estimates its membership at roughly 5 million globally — about 0.07 percent of the world population — making it one of the rarest common birthdays, exceeded in rarity only by December 25 and January 1, which hospitals and parents actively avoid through scheduled delivery timing.

Frequently Asked Questions

Why is the leap year rule three conditions rather than just “every four years”?

The three-part rule exists because the solar year is 365.2422 days, not exactly 365.25. Adding a leap day every four years overshoots by 0.0078 days per year. Skipping century years removes three leap days per 400 years, and restoring every 400th year adds one back, producing an average of 365.2425 days — within 26 seconds of the true solar year.

Was the year 2000 a leap year?

Yes. The year 2000 satisfied all three Gregorian conditions: divisible by 4, divisible by 100, and divisible by 400. Many people mistakenly believed 2000 would not be a leap year because of the century-year exception, but the 400-year override applies. The next century year that will NOT be a leap year is 2100.

How many days does the Gregorian Calendar add per 400-year cycle?

Exactly 97 leap days per 400-year cycle. That works out to 365.2425 days per average year. Over those 400 years, the total calendar contains 146,097 days — a number that conveniently divides into exactly 20,871 weeks, meaning the Gregorian Calendar repeats its day-of-week pattern precisely every 400 years.

Did the switch to the Gregorian Calendar cause social unrest?

In Britain, the 1752 transition produced documented complaints from workers who felt cheated out of 11 days of wages or rent periods. The phrase “Give us our eleven days” appears in contemporary pamphlets and is depicted in William Hogarth’s 1755 painting An Election Entertainment. However, most historians characterize the unrest as limited rather than widespread rioting, which was a later popular myth.

How accurate is the Gregorian Calendar long-term?

The residual error is approximately 26 seconds per year, accumulating to one full day of drift in roughly 3,300 years. For context, the Julian Calendar drifted one full day every 128 years. No correction to the Gregorian system is currently scheduled or considered necessary; by the time a fix would be needed, the slowing of Earth’s rotation will likely have shifted the target figure anyway.

References

1. Richards, E.G. Mapping Time: The Calendar and Its History. Oxford University Press, 1998.
2. Seidelmann, P. Kenneth (ed.). Explanatory Supplement to the Astronomical Almanac. University Science Books, 1992. https://aa.usno.navy.mil/publications/docs/exp_supp.php
3. International Earth Rotation and Reference Systems Service. “Bulletin C — Leap Seconds.” IERS, 2023. https://www.iers.org/IERS/EN/Publications/Bulletins/bulletins.html

Frequently Asked Questions