Finding a turning point
An apsis occurs where the changing Earth-Moon distance reaches a local low or high. Each event is paired with its instant and distance; a midnight-only reading can fall before or after the actual turning point.
A previous apsis occurs before the input and a next apsis after it. Perigee and apogee alternate, and separate pairs let readers compare like with like.
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 distance because orbital perturbations make successive extrema unequal. Event-specific kilometres are therefore more meaningful than one standard perigee value and one standard apogee value for every lunation.
Worked example
Worked apsis example
Starting from 26 August 2026 at 12:00 UTC, these extrema bracket the input:
- 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. Distance minimum and annual extremity are separate comparisons.
Read before comparing
Reference conditions
- Apsis times and distances use an Earth-centred reference frame; local apparent size at a horizon uses an observer-centred frame.
- Previous, next, and nearest identify the events around the selected instant rather than a monthly or yearly schedule.
- Definitions of “supermoon” vary; perigee and apogee dates and distances let readers apply their chosen convention.
Next step
Use the working calculator
Calculate another exact instant with the same reference frame and conventions described on this working sheet.