A micromoon is a full moon that happens when the Moon is at or near apogee, the farthest point of its orbit from Earth. Because it's farther away, it looks slightly smaller and dimmer than usual: roughly an eighth to a seventh smaller across than a supermoon, and only about a fourteenth smaller than a full moon at average distance. Like "supermoon," it's a popular term rather than an official astronomical one, and most people can't see the difference without a side-by-side photo.
How far away is the Moon at a micromoon?
The Moon's orbit is an ellipse, not a circle, so its distance from Earth changes through every orbit. NASA gives typical figures of about 226,000 miles (363,300 kilometers) at perigee, the closest point, and about 251,000 miles (405,500 kilometers) at apogee, the farthest. The exact numbers vary a little from one orbit to the next, because the Sun's gravity tugs the orbit out of shape.
A full moon can happen anywhere along that ellipse. When it falls close to perigee, headlines call it a supermoon. When it falls close to apogee, it's a micromoon. Astronomers would more formally call it an apogee full moon, and you'll also see "minimoon" in some places. All three mean the same thing.
How much smaller and dimmer does it look?
Less than you might think. Using the figures collected by EarthSky, a micromoon looks about an eighth to a seventh smaller across than a supermoon, and about a fourteenth smaller than a full moon at average distance.
Brightness changes more noticeably than size, because the lit area shrinks in two directions at once. NASA notes that the full moon can appear nearly a third brighter at its best than the faintest full moon of the year, and a micromoon is, by definition, that faint end of the range.
What does that look like in practice?
- Overhead, on its own, a micromoon looks like any other full moon. There's nothing nearby to compare it with, and our memory for the size of the Moon is poor.
- In photographs, the difference is clear. Shoot a supermoon and a micromoon with the same lens at the same zoom and put them side by side, and the micromoon is visibly smaller.
- On the horizon, a rising micromoon can still look enormous, because the moon illusion, a trick of perception, is far stronger than the real change in distance. We explain that in why does the moon look bigger.
Why micromoons come round about seven months after supermoons
The Moon takes about 27.5 days to travel from one apogee to the next, but about 29.5 days to go from one full moon to the next. Because the two cycles don't match, the full moon creeps around the orbit a little each month. For a few months running, full moons land near perigee, then they drift toward apogee, then back again. The whole pattern repeats roughly every thirteen and a half months.
Apogee is on the opposite side of the orbit from perigee, so the micromoons come about halfway through that pattern, roughly seven months after a run of supermoons. Most years have one or two full moons that count as micromoons, depending on whose cutoff you use. The full moon calendar lists the dates and signs of the next twelve full moons; our guide to what a supermoon is covers the other end of the range.
Who decides what counts as a micromoon?
Nobody officially. Because the term isn't defined by any astronomical body, different sources draw the line in different places. EarthSky notes two common versions:
- A fixed distance. One widely used rule, from the timekeeping site timeanddate.com, counts a full moon as a micromoon if the Moon's center is farther than 405,000 kilometers from Earth's center.
- A percentage of the orbit. Another, used by the eclipse expert Fred Espenak, counts a full moon that falls in the farthest tenth of that orbit's range of distances, which works out to a slightly looser limit on average.
So one calendar may list a micromoon where another lists none. That's not a mistake on either side; they're using different yardsticks for an informal label.
The micro new moon and the ring of fire
A new moon can fall near apogee too. You can't see a new moon, so a "micro new moon" usually passes unnoticed, except in one case: a solar eclipse.
During a solar eclipse, the new moon passes directly in front of the Sun. If the Moon is near perigee, it looks large enough to cover the Sun completely, and you get a total eclipse. If it's near apogee, it looks slightly smaller than the Sun, so it can't quite cover it. NASA's Earth Observatory describes the result: a bright ring of sunlight, sometimes called a ring of fire, left around the Moon's dark disc. That's an annular eclipse, and it happens because of the same distance effect that makes a micromoon. Looking at any part of the Sun requires proper eclipse glasses or a projection method; a ring of fire is still bright enough to damage your eyes.
There's a quieter effect at the coast. The Moon's pull on the oceans is weaker when it's farther away, and NOAA notes that tidal ranges are smaller than average around apogee. A full or new moon near apogee still brings spring tides, just slightly gentler ones. Our guide to how the moon affects tides explains why.
Micromoons in astrology
The word "supermoon" was coined by the astrologer Richard Nolle in 1979, and "micromoon" followed later as its opposite. Astrologers who give weight to supermoons sometimes read a micromoon as a softer, quieter full moon, with its themes turned down rather than up. Many other astrologers don't use either term, since traditional astrology has no doctrine of lunar distance. Either way, the meaning still comes first from the sign and house the full moon falls in.
There is one apogee idea that is well established in modern astrology. The point in space where the Moon reaches apogee is called Black Moon Lilith, and some astrologers place it in birth charts as a sensitive point. It isn't an object, and it isn't connected to micromoons in meaning, but it's the same far end of the same orbit. Read more in Black Moon Lilith in astrology.
Questions readers ask
How often is there a micromoon?
Usually once or twice a year, about seven months after the year's supermoons. The exact count depends on the definition, since there's no official distance cutoff.
Can you tell a micromoon just by looking?
Not reliably. Without anything to compare it with, a micromoon looks like an ordinary full moon. The difference shows up in photographs taken with the same camera settings, and it's a little dimmer.
Is a micromoon the same as a minimoon?
Yes. Micromoon, minimoon and apogee full moon are three names for the same thing: a full moon close to the Moon's farthest point from Earth.
Does a micromoon affect tides or mood?
It brings slightly smaller tides than a full moon at average distance, because the Moon's pull is a little weaker. There's no good evidence that it affects mood, and the same goes for supermoons and full moons in general, as we cover in does the moon affect your mood.
