A supermoon happens when a full Moon coincides with the Moon being at or very near its closest point to Earth in its elliptical orbit, called perigee. This combination makes the Moon appear larger and brighter than average, though the effect is modest (typically about a 14% increase in apparent size and a small rise in brightness). The event can occur several times in a year, depending on the Moon’s orbital geometry and the alignment with perigee. Key factors

• Moon’s orbit is not a perfect circle: perigee (closest approach) and apogee (farthest distance) vary month to month.
• Full Moon phase: the Moon is fully illuminated by the Sun roughly every 29.5 days, which pairs with perigee only occasionally.
• The most noticeable size and brightness boost occurs when a full Moon happens near perigee.

Common questions

• Do supermoons affect tides? Yes, but the difference is usually small. Tides are strongest when a full Moon or new Moon coincides with perigee and other gravitational factors (often called spring tides), but the incremental tidal increase during a supermoon is typically only a few centimeters to inches.
• Are all full Moons supermoons? No. A supermoon requires both a full Moon and a perigee close to that full Moon; not all full Moons meet this condition.

If you’d like, I can tailor this explanation to a specific upcoming date and tell you whether a supermoon is expected then, plus tips for observing or photographing it.