Moon vs. Supermoon: What's Different

The core difference between an average Full Moon and a supermoon comes down to one number: distance. The Moon's elliptical orbit takes it anywhere from about 356,500 km (perigee, closest) to about 406,700 km (apogee, farthest) from Earth. An average Full Moon sits somewhere in between; a supermoon is specifically a Full Moon occurring at or near perigee.

Put the two numbers side by side and the gap is modest but entirely real: at perigee the lunar disc spans about 14% more sky than it does at apogee, and it throws roughly 30% more light. Neither figure is an estimate. Angular diameter follows directly from distance, and brightness follows from the inverse-square law applied to that same distance, which is why the two percentages stay stable across sources even when those sources disagree about what to call the event.

To the naked eye, though, that arithmetic oversells the experience badly. A Full Moon hanging alone in the sky offers no reference object, so the eye has nothing to measure it against — and low on the horizon, any size impression gets swamped by the Moon illusion, a perceptual effect that inflates every Full Moon regardless of where it sits in its orbit. The percentages are honest. The impression they set up in a reader's head usually isn't, which is most of why supermoon coverage disappoints people who go outside expecting a spectacle.

One difference in this comparison doesn't depend on the eye at all. A nearer Moon pulls harder on the oceans, so the tides bracketing a perigee Full Moon run a little above their usual spring range — perigean spring tides, in the technical vocabulary. The margin is centimeters, not meters, and coastal communities notice it mainly when it coincides with a storm surge. Small as it is, it's the one item on this list that would still show up in the data if nobody were watching the sky at all.

Frequency is where the comparison gets genuinely slippery. Three or four Full Moons in a typical year clear the bar, but the count moves depending on which cut-off a given publication has adopted, so two outlets can report different supermoon totals for the same year without either being wrong. This site's supermoon guide sets out how the competing thresholds are drawn; the year-ahead roundup on the blog lists the dates themselves.

A useful mental benchmark for the actual size difference: a supermoon compared to an apogee full moon is roughly comparable to the size difference between a US quarter and a US nickel held at the same distance — noticeable in a direct side-by-side comparison, but easy to miss without one.

Because supermoon media coverage has become an annual, sometimes multiple-times-a-year event, some astronomy communicators have pushed back on the term's overuse, arguing that treating 3-4 ordinary occurrences a year as headline news dilutes public understanding of genuinely rarer astronomical events like eclipses.

Astronomy hobbyist forums and social media groups often share real side-by-side comparison photos from actual supermoon and apogee events, a good resource for seeing the genuine (rather than described) size difference for yourself.

It's also worth clarifying a common point of confusion: "supermoon" and "micromoon" (the apogee equivalent, sometimes called a minimoon) are the two ends of the same distance spectrum, not two separate special categories — every full moon technically falls somewhere between these two extremes, with most landing in an unremarkable middle range that neither term describes.

Because the percentage differences involved (roughly 14% size, 30% brightness) are real but modest, the most reliable way to actually perceive the difference remains a controlled side-by-side comparison rather than casual naked-eye observation on two separate, unconnected nights months apart, when memory and differing atmospheric conditions make an accurate mental comparison genuinely difficult.

For readers who want a single memorable number: the roughly 50,000-kilometer swing between the Moon's closest and farthest orbital points is the entire physical basis for every supermoon claim — everything else is a description of how that distance change translates into apparent size and brightness.

Astronomy news sites and apps that specifically flag each year's closest and farthest full moons make it easy to know in advance which occurrence in a given year represents the most extreme comparison point, without needing to calculate orbital distances yourself.

A useful annual habit: note this year's specific closest and farthest full moon dates from this site's calendar, then revisit the comparison next year to see how the specific dates shift.

Keeping a simple photo log across a full year, noting the date and distance of each full moon you photograph, builds your own personal reference for future comparisons.

Revisiting this comparison each time a new supermoon is announced helps keep the real numbers fresh rather than relying on memory of a previous year's explanation.

Perigee and apogee, the two orbital extremes driving this entire comparison, are explained in their own right on this site's supermoon guide.

The real numbers, once known, replace guesswork with genuine understanding.

Comparison beats description every time.

Side by side tells the truth.

The numbers rarely lie.