Moon Distance Calculator

How It Works

The Moon follows an elliptical orbit around Earth. This calculator estimates its distance for any date using the mean distance (384,400 km) adjusted by the lunar anomalistic cycle — the periodic variation in distance caused by the elliptical orbit. The Moon completes one anomalistic cycle (perigee to perigee) every approximately 27.55 days, independent of the 29.53-day phase cycle. The result is shown in both kilometers and miles, with a label indicating whether the Moon is near perigee, apogee, or average distance.

Distance Reference Values

Why Does Distance Change?

The Moon's orbit around Earth is an ellipse with Earth at one focus. This means the Moon is closer to Earth at one end of its orbit (perigee) than the other (apogee). The ratio of closest to farthest distance is about 0.88 — a 13% variation over one anomalistic cycle. This variation is caused primarily by the gravitational tug of the Sun, which perturbs the Moon's orbit and slowly rotates the orbital ellipse over time (the line of apsides rotates once every ~8.85 years).

Practical Effects of Distance

Distance affects three observable properties: angular size (the Moon at perigee appears about 14% larger in diameter than at apogee), brightness (about 30% brighter at perigee), and tidal strength (tidal force varies as the inverse cube of distance — a 13% change in distance produces about a 44% change in tidal force compared to apogee). The angular size difference, while real, is difficult to judge without a reference photograph. The tidal effect is measurable in tidal gauge records.

Perigee, Apogee, and the Supermoon Connection

When a full moon coincides with perigee (or near-perigee), it is called a Supermoon — visually the largest full moon of the year. When a full moon coincides with apogee, it is a Micromoon — the smallest. The alignment of these two cycles (synodic 29.53 days and anomalistic 27.55 days) slowly drifts, producing a longer "supermoon season" every 1–2 years when several consecutive full moons are near perigee. Use our Supermoon Calculator to find upcoming supermoon dates.

Frequently Asked Questions

How far is the Moon from Earth?

The average (mean) Earth-Moon distance is 384,400 km (238,855 miles), measured center-to-center. It ranges from approximately 356,500 km at closest approach (perigee) to 406,700 km at farthest point (apogee) — a difference of about 50,200 km (31,200 miles).

How long does light take to travel from the Moon to Earth?

At mean distance, moonlight takes about 1.28 seconds to reach Earth (384,400 km ÷ 299,792 km/s). At perigee it is about 1.19 seconds; at apogee about 1.36 seconds. Radio signals sent to and from Apollo astronauts on the Moon had a round-trip delay of about 2.5 seconds.

What is a Supermoon?

A Supermoon is a full moon that occurs near perigee — typically when the Moon is within about 367,000 km of Earth. It appears up to 14% larger in diameter and about 30% brighter than a full moon at apogee (sometimes called a Micromoon). See our Supermoon Calculator for upcoming dates.

Does the Moon's distance affect us physically?

Tidal force (the force responsible for ocean tides) varies with the inverse cube of distance, so a 13% change in distance produces roughly a 44% change in tidal force between perigee and apogee. In practice, this means perigean spring tides (during a near-perigee full or new moon) are noticeably stronger than typical spring tides, which can matter for coastal flood risk in vulnerable areas.

How accurate is this distance estimate?

This calculator uses a simplified single-harmonic model of the lunar orbit. The true lunar orbit is much more complex, with dozens of perturbation terms from the Sun and planets. For precise astronomical work, use an ephemeris service such as NASA's JPL Horizons. For general interest and planning purposes, this tool is accurate to within a few thousand kilometers.