Supermoon & Micromoon Calendar 2026–2030

Supermoon and Micromoon

A reference guide to perigee and apogee syzygies — what they are, the orbital mechanics behind them, and how much of the "supermoon" phenomenon is real versus overstated.

A supermoon is a New or Full Moon that occurs near perigee, the point in the Moon's elliptical orbit closest to Earth. A micromoon is the opposite: a New or Full Moon occurring near apogee, the orbit's farthest point. The Moon's geocentric distance varies by roughly 42,000 km between mean perigee and mean apogee, so a perigee Full Moon can appear measurably larger and brighter than an apogee Full Moon — though, as covered below, "measurably" and "noticeably to the naked eye" are not the same thing.

Neither term is a formal astronomical classification. Astronomers and institutions such as NASA do use "supermoon" in public communication, but the underlying event is more precisely described as a perigee syzygy or apogee syzygy — "syzygy" being the alignment of Sun, Earth, and Moon that defines a New or Full Moon. "Supermoon" and "micromoon" are popularizations that entered common use decades after the underlying orbital mechanics were already well understood.

1. Etymology and Terminology

The word "supermoon" was coined in 1979 by American astrologer Richard Nolle, writing in Dell Horoscope magazine. Nolle defined it as a New or Full Moon occurring at or near — within about 90% of — its closest approach to Earth in a given orbit. The term saw little use for decades and only entered mainstream media circulation around 2011.

Because of its astrological origin, "supermoon" has never been adopted as an official term by the International Astronomical Union. Ephemeris sources such as Fred Espenak's tables use the more precise perigee syzygy and apogee syzygy. In practice, the popular and technical terms describe the same physical event.

2. Orbital Mechanics

The Moon's orbit around Earth is an ellipse with a mean eccentricity of 0.0549, not a circle. Its geocentric distance therefore varies continuously, from a mean of 363,396 km at perigee to a mean of 405,504 km at apogee — a difference of roughly 42,000 km, or about 11.6% of the mean perigee distance. Because of gravitational perturbations from the Sun on the Moon's already-eccentric orbit, the exact distance of any given perigee or apogee shifts from one orbit to the next. Over the 5,000-year span from 2000 BCE to 3000 CE, the closest perigees range from 356,355 km to 370,399 km, and apogees from 404,042 km to 406,725 km — meaning the "supermoon" and "micromoon" thresholds are themselves moving targets.

Whether a given New or Full Moon counts as a supermoon or micromoon is defined quantitatively, using the fraction of the perigee-to-apogee distance the Moon has covered at that phase. Under the commonly used 90% convention that Espenak's tables apply, a New or Full Moon qualifies as a supermoon when it falls within the closest 10% of that range to perigee, and as a micromoon when it falls within the farthest 10% near apogee. (Espenak's own supermoon and micromoon tables express this fraction from opposite ends — one anchored at perigee, the other at apogee — so a single formula copied from either table in isolation can be misleading; the 90%-of-range description above holds either way.)

Supermoons and micromoons also follow a predictable ~413-day repetition cycle. A synodic month (New Moon to New Moon) averages 29.53059 days, while an anomalistic month (perigee to perigee) averages 27.55455 days. Fourteen synodic months (413.428 days) very nearly equal fifteen anomalistic months (413.318 days), so a Full Moon near perigee recurs at close to the same point in the orbit roughly every 413 days. This is also why a full supermoon is often preceded or followed, about two weeks later, by a new micromoon, and vice versa: the line connecting perigee and apogee (the line of apsides) is pointed toward the Sun at those times.

3. Quantifying the Effect

The oft-cited figures of "up to 14% larger and 30% brighter" are approximations comparing the most extreme perigee and apogee distances, not typical month-to-month variation. They can be derived directly from orbital geometry and basic photometry.

Apparent size

The Moon's apparent angular diameter is inversely proportional to its distance. Ephemeris tables put a near-extreme perigee Full Moon's diameter at about 33.4 arcminutes, versus about 29.4 arcminutes for a near-extreme apogee Moon:

Apparent brightness

Brightness follows the inverse-square law of light propagation: received flux scales as 1/d². Using the 2016 record perigee (356,523 km) against a representative extreme apogee (~406,700 km):

Both figures represent the ceiling of the effect, comparing the closest realistic perigee to the farthest realistic apogee. Compared with an average Full Moon — the more common real-world comparison — the difference in size and brightness is smaller than this maximum perigee-to-apogee comparison suggests.

4. Perceptibility and the Moon Illusion

Despite the percentages above, the difference is difficult to judge reliably when a supermoon is viewed by itself, high in an empty sky, without a direct side-by-side comparison or a familiar reference point.

The Moon does often look dramatically larger near the horizon — but this is a separate, unrelated effect called the Moon illusion: foreground objects like trees, buildings, and terrain give the brain a size reference it doesn't have when the Moon is high overhead. NASA notes this is a genuine optical/perceptual illusion, not a change in the Moon's actual angular size, and its underlying cause is still debated among vision scientists. A supermoon at moonrise combines both effects — a real, small distance-driven size increase plus the much larger illusory one — which is largely why supermoons photograph and "feel" so much more dramatic near the horizon than their true 14% would suggest.

5. Tidal Effects

Unlike apparent size and brightness, the tidal effect of a supermoon is real and physically well characterized. Ordinary gravitational attraction follows an inverse-square law, but the tide-generating force (the differential pull across Earth's diameter) follows an inverse-cube law: it scales with 1/d³, not 1/d². Using the Moon's mean distance (~384,400 km) against its mean perigee distance (363,396 km), this puts the tide-generating force at perigee at roughly 19% stronger than at the Moon's average distance — a larger effect than the inverse-square law alone would suggest. This cube-law sensitivity is also why the Moon, despite being about 27 million times less massive than the Sun, generates roughly twice the Sun's tidal effect: it is close enough that the cube-law distance advantage overwhelms the Sun's mass advantage.

When perigee coincides with New or Full Moon, the Moon's closer distance strengthens this already-largest tide of the month (a spring tide), producing what's called a perigean spring tide. Popular sources sometimes call unusually high tides "king tides," but that term is used more broadly for exceptional seasonal high water and isn't strictly interchangeable with "perigean spring tide." The increase in tidal range is real, but its size varies substantially by location — local coastline shape and the normal tidal range there both affect how much difference it makes, from a few centimeters in some places to over a foot in others. In practice it matters most as a contributing factor to coastal flooding when a perigean spring tide coincides with a storm surge, rather than as a dramatic effect on its own.

6. Notable Events

Note that 2016 is the closest full moon so far this century, not the closest overall — Espenak's tables project several later 21st-century full moons, including 2034 above, to come slightly closer.

7. Common Misconceptions

Source for lunar distance data: Espenak, F. — AstroPixels.com

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