A supermoon is a full Moon that appears larger and brighter in the sky because it coincides with the Moon’s closest approach to Earth in its elliptical orbit, known as perigee. In other words, when a full Moon happens near perigee, it looks bigger than a typical full Moon. Key points:

• Perigee proximity: The Moon’s orbit is not a perfect circle; its distance from Earth varies. A supermoon occurs when the full Moon coincides with a perigee passage, bringing it closer than usual. This combination makes the Moon appear up to about 10-14% larger and up to roughly 30% brighter than average full Moons, though the exact visual difference can be subtle to the naked eye and is sometimes amplified by the Moon-illusion effect when near the horizon.

• Frequency: Because the Moon’s orbit is elliptical and its alignment with Earth and the Sun shifts over time, supermoons are periodic but not guaranteed every lunar cycle. They occur when two conditions align: a full Moon and a relatively close perigee.

• Related terms: A “supermoon” can coincide with special events such as a total lunar eclipse (supermoon during an eclipse, sometimes called a “super blood moon”) or a blue moon (two full Moons in one calendar month) when the timing aligns. These are not separate phenomena but combinations of the Moon’s orbit with its phase.

• Observational impact: The gravitational interaction during perigee can enhance tides, but the tidal effects are usually not extreme or dangerous in most locations. The moon’s apparent size is what most people notice, rather than a dramatic physical difference.

Common nuances and misconceptions:

• Size vs. brightness: The apparent size increase is real but modest; the brightness boost is a result of closer distance and atmospheric effects. The popular perception of a dramatically larger Moon is often influenced by the Moon illusion.

• No universal definition: There is no single formal scientific mandate for what counts as a supermoon, but the working idea is a full Moon that also occurs near Earth’s perigee. Different sources may use slightly different distance thresholds.

• Variations in terms: Some sources distinguish “supermoon” from “perigee-full Moon” or simply describe full Moons that are unusually close to Earth; others include occasional informal subcategories like “super blue moon” or “super blood Moon” when specific eclipse or calendar coincidences occur.

If you’d like, I can tailor this to a local viewing guide (best dates for your hemisphere, rise/set times, and naked-eye visibility) or provide quick comparisons with related lunar events.