The mainstream scientific consensus defines a supermoon as a full moon that occurs when the Moon is at or near its closest point to Earth (perigee) in its elliptical orbit, happening roughly every 13-14 months. This alignment makes the Moon appear approximately 14% larger in diameter and up to 30% brighter compared to when it is at apogee. Astronomers note that the term 'supermoon' was coined by astrologer Richard Nolle in 1979 but has been adopted in popular media, while scientists prefer 'perigee full moon' for precision. The phenomenon is predictable using orbital mechanics and does not deviate from standard lunar cycles.
Observable Effects
From Earth, a supermoon offers a visually striking view, particularly when rising or setting, due to the Moon illusion enhancing its apparent size. However, the actual increase in brightness and size is modest and best appreciated through side-by-side comparison with average full moons. Reliable sources like timeanddate.com confirm these effects are measurable but subtle for casual observers without optical aid. (https://www.timeanddate.com/astronomy/moon/super-full-moon.html)
Lack of Significant Impacts
Mainstream experts from institutions like NASA emphasize that supermoons produce no extraordinary effects on Earth, such as triggering earthquakes, extreme weather, or unusually high tides beyond normal variations. Tidal forces may increase slightly but remain within predictable ranges. Claims linking supermoons to disasters lack empirical support and stem from coincidence rather than causation, as confirmed by astronomical analyses.
Conclusion
In summary, supermoons represent a routine yet visually appealing aspect of lunar astronomy that is often exaggerated in popular culture but holds limited scientific novelty beyond orbital dynamics.
Alternative Views
"Supermoon" is an astrological term, not an astronomical one
Many astronomers argue that "supermoon" isn't really a science term at all. The astrologer Richard Nolle coined it in 1979 for a new or full moon that falls within 90% of the Moon's closest approach to Earth (perigee). It is an arbitrary cutoff, and there is no agreed definition. Different outlets therefore count three or four supermoons in a year where others count fewer. Astronomers prefer "perigee full moon" or "perigee-syzygy". On this view, popular astronomy coverage has taken up an astrologer's word with a fuzzy meaning and treats it as if it described a precise event ((https://en.wikipedia.org/wiki/Supermoon)).
Attributed to: Richard Nolle (who coined the term); astronomers and science writers such as Phil Plait (Bad Astronomy) who have criticised the label; the Wikipedia article notes that 'perigee-syzygy' is the scientific term
The hype overstates what you can actually see
A perigee full moon looks only about 7% larger and 15% brighter than an average full moon. Compared with the smallest full moon of the year (the 'micromoon'), it is about 14% larger and up to 30% brighter. Skeptics say that without a side-by-side comparison, the human eye can't tell the difference. The dramatic 'huge moon' feeling mostly comes from the Moon illusion near the horizon and from telephoto photography. Critics argue that heavy promotion sets people up for disappointment and teaches them the wrong lessons about perception.
Attributed to: Phil Plait; Joe Rao (Space.com/SkyandTelescope contributors); timeanddate.com explainers note the modest size difference ((https://www.timeanddate.com/astronomy/moon/super-full-moon.html))
Supermoons trigger earthquakes and disasters
Nolle and his followers claim that the extra gravitational pull at perigee raises the risk of earthquakes, volcanic eruptions and extreme weather. They point to the 2011 Tōhoku earthquake, which happened about a week before a supermoon. Some peer-reviewed work gives a narrow version of this some support. Ide, Yabe and Tanaka (Nature Geoscience, 2016) found that very large quakes may be slightly more likely when tidal stress is high. Mainstream seismologists say any such effect is tiny and can't be used for prediction.
Attributed to: Richard Nolle; partial support from Satoshi Ide et al. (2016); disputed by USGS seismologists
Real but practical effects: king tides and coastal flooding
Some focus on a real effect that the 'looks bigger' coverage underplays. When a perigee full or new moon lines up with the Sun, it produces perigean spring tides, or 'king tides'. As sea levels rise, these tides increasingly cause nuisance flooding in places like Miami and Norfolk. Advocates argue that supermoon coverage should be about flooding risk rather than how the Moon looks.
Attributed to: NOAA tides scientists (e.g., William Sweet); King Tides Project citizen-science groups
Spiritual and behavioural significance
Astrologers and some New Age practitioners see supermoons as times of heightened emotion, endings or new beginnings. Some ER staff and police also say they are busier around full moons. Studies, including a meta-analysis by Rotton and Kelly (1985), generally find no such effect. Even so, believers treat the supermoon as culturally and personally meaningful.
Attributed to: Astrologers such as Susan Miller (Astrology Zone); contrasted by researchers James Rotton and Ivan Kelly
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