Moon Distance and Angular Size
See how geocentric Earth-Moon distance determines the Moon's modeled angular diameter, with an exact-instant calculation and interpretation limits.
Moon distance calculation methods
The Earth-Moon separation changes continuously because the lunar orbit is not a perfect circle. The distance tool evaluates that geometry for one resolved UTC instant and then performs separate event searches for the neighboring minimum and maximum distances.
This section divides instantaneous geometry from orbital turning points. Distance and angular size describe the selected moment. Perigee and apogee are local extrema that require searching around it. The two leaves explain why a current reading cannot by itself identify an apsis and why apparent size must state its observer convention.
How this calculation is divided
The reported distance is geocentric: center of Earth to center of Moon. Apparent angular diameter is the modeled width of the lunar disc from Earth's center at that distance. Sub-Earth libration and geocentric ecliptic coordinates supply additional geometry but do not turn the result into an observing forecast.
For apsides, the engine enumerates distance extrema on both sides of the input. Previous and next perigee and apogee remain distinct result pairs. The nearest event is chosen by elapsed time, so it need not be the event with the smallest or largest distance among all values shown.
Two technical guides
Lunar Perigee and Apogee Calculation
Learn how lunar perigee and apogee are found as local geocentric distance extrema, and how previous, next, and nearest apsides are selected.
Scope boundaries
- This section does not publish perigee, apogee, or “supermoon” schedules by month or year.
- Geocentric apparent size is not a camera-image measurement and does not include a local horizon illusion.
- Observer-specific topocentric distance and altitude belong to the position calculator.
Use the working calculation
Open the Moon Distance Calculator to evaluate another exact instant with the production logic described here. For the shared time model, accuracy policy, and supported era, return to the methodology overview. The implementation and independent references are listed on the sources page.