How lunar perigee and apogee are calculated
Perigee is a local minimum in the geocentric Earth-Moon distance; apogee is a local maximum. They are events with timestamps, not permanent distance bands and not labels that can be assigned reliably from a single rounded reading.
The distance calculator searches the modeled orbit around the selected instant. It returns one previous and one next event of each type, then identifies which of those four is nearest in time. That structure preserves the orbital sequence without turning the site into an apsis calendar.
Finding a turning point
An extrema search follows how distance changes until it reaches a local low or high. Merely sampling midnight values can miss the true turning time or select the wrong day, while choosing the smallest displayed value in a short table says nothing about what happened just outside the table. The astronomy engine's apsis search supplies the event instant and modeled distance together.
Strict bracketing is part of the result contract. A previous apsis must occur before the input and a next apsis after it. Perigee and apogee alternate, but the interface keeps separate pairs so users can compare like with like instead of assuming that the next event of any kind answers a request for the next perigee.
Nearest means nearest in time
The nearest-apsis label compares absolute elapsed time from the selected instant to each returned event. It does not mean the closest Moon, the most extreme perigee, or the largest apparent disc in a year. A previous apogee can be the nearest event even though a future perigee has a much smaller distance.
Each perigee and apogee has its own modeled distance because the orbit is perturbed and successive extrema are not identical. The method therefore reports event-specific kilometres rather than attaching one standard perigee value and one standard apogee value to every lunation.
Worked apsis-search example
Starting from 26 August 2026 at 12:00 UTC, the production search brackets the input with these relevant extrema:
- Previous apogee
- 22 August 2026, 08:21 UTC — 404,632 km
- Next perigee
- 6 September 2026, 20:44 UTC — 368,249 km
- Next apogee
- 19 September 2026, 03:00 UTC — 404,210 km
- Nearest apsis
- the previous apogee, by elapsed time
The nearest label belongs to the 22 August apogee because it is temporally closest to the input. It does not describe a distance minimum, and it makes no claim that this apogee is the largest or most important of the year.
Calculation limits
- Apsis results are geocentric model events, not forecasts of local apparent size at a horizon.
- The page explains a calculation method and intentionally provides no monthly or yearly event schedule.
- Terms such as “supermoon” depend on external naming conventions and are not calculation outputs here.
Use the working calculator
Open the Moon Distance Calculator to calculate another exact instant with the same production logic. The calculator accepts the relevant input and keeps result state on its single canonical tool page.