Real-World Use Cases

Astrophotographers plan their moon shots around lunar distance. When the moon is at perigee (closest to Earth), it appears about 14% larger in angular diameter than at apogee. A photographer in Cape Town planning a moonrise panorama over Table Mountain on July 21, 2026 (perigee day) knows the moon will appear roughly 33.4 arcminutes wide, making for a dramatic foreground composition.

Amateur astronomers observing the moon through a telescope benefit from knowing the distance. At perigee, craters and maria appear slightly larger and easier to resolve. A observer in London using a 4-inch refractor can see more detail along the terminator when the moon is 356,000 km away compared to 406,000 km at apogee.

Science educators explaining supermoons need accurate distance data. A supermoon occurs when a full moon coincides with perigee. On November 5, 2025, the full moon was at approximately 360,000 km, appearing noticeably brighter and larger. The calculator lets teachers show the exact distance and compare it to an average full moon.

Tide prediction enthusiasts use lunar distance to understand spring tide variation. Tides are strongest near perigee because gravitational pull increases with proximity. A surfer in Sydney checking the moon distance for December 12, 2026 can confirm whether the upcoming perigee alignment will produce the king tides that create notable surf conditions.

Satellite operators and space mission planners track lunar distance for orbital mechanics. The moon's gravitational sphere of influence changes with distance, affecting satellite trajectories. While professional missions use certified ephemeris data, the calculator provides a quick reference for educational purposes and rough planning.

How It Works

The calculator uses the SunCalc library's getMoonPosition function, which returns the moon's distance in kilometers based on standard lunar ephemeris calculations. The distance varies continuously because the moon's orbit is elliptical, not circular.

The moon's average distance from Earth is about 384,400 km. The closest point in the orbit is called perigee (typically around 356,500 km) and the farthest is apogee (typically around 406,700 km). The difference of about 50,000 km means the moon's apparent size in the sky changes by roughly 14% between these two extremes.

To find upcoming perigee and apogee dates, the calculator samples the moon's distance at regular intervals over the next 60 days and identifies the local minima (perigee) and maxima (apogee). This approach is accurate to within a few hours for most purposes. The moon completes one orbit in about 27.3 days, so perigee and apogee each occur roughly once per month.

The distance chart plots the moon's distance over a 30-day window centered on the selected date. The curve is smooth and sinusoidal, reflecting the elliptical orbit. The amplitude of the curve shows the difference between perigee and apogee for that particular orbit, which varies slightly from cycle to cycle due to perturbations from the sun's gravity.

Step-by-Step Usage Guide

1. Select a city from the preset list or enter custom latitude and longitude coordinates. Distance is calculated relative to the center of the Earth, so location has a minor effect (up to 6,378 km for surface vs. center).
2. Click 'Use my location' to auto-fill coordinates from your device's GPS if available.
3. Pick a date using the date picker. The calculator defaults to today.
4. Read the current moon distance display showing kilometers and miles, plus the angular diameter for telescope and photography planning.
5. Check the perigee and apogee cards to see when the moon will be closest and farthest in the coming weeks.
6. Scroll down to the distance chart to see how lunar distance varies over a 30-day window, with the selected date marked.
7. Compare the selected distance to the average, minimum, and maximum distances to understand where the moon is in its orbital cycle.

Examples

Common Mistakes and Edge Cases

Things to watch out for

• Perigee and apogee are not exactly monthly: The moon's orbital period relative to the stars (sidereal month) is 27.3 days, but perigee to perigee (anomalistic month) is about 27.55 days. This means perigee dates shift slightly earlier each calendar month.
• Supermoon is not a strict astronomical term: There is no single official definition. Most sources define it as a full moon within 90% of perigee, but some use 361,000 km or 362,000 km as the threshold. Different sources may disagree on whether a particular full moon qualifies.
• Distance is measured center-to-center: The distance shown is between the center of the Earth and the center of the moon. Your actual distance from the moon depends on your location on Earth's surface and can vary by up to 6,378 km (Earth's radius). At moonrise, you are roughly 6,378 km farther from the moon than when it is directly overhead.
• Angular diameter depends on distance: The moon's apparent size in the sky is inversely proportional to its distance. At perigee, the angular diameter is about 33.5 arcminutes. At apogee, it is about 29.4 arcminutes. This 14% difference is visible to the naked eye when comparing photos.
• The chart uses daily samples: The distance chart samples the moon's distance once per day over a 30-day window. The actual distance curve is continuous, so the exact perigee or apogee time may fall between sample points. For precise timing, use a dedicated ephemeris tool.
• Lunar distance does not directly cause seasons: The moon's distance affects tides and apparent size, but Earth's seasons are caused by axial tilt, not lunar distance. Do not confuse lunar perigee with seasonal changes.

FAQ

Related Tools

Data Sources and Accuracy