What algorithm is used for moon calculations?

This tool uses the low-precision lunar position algorithm from "Astronomical Algorithms" by Jean Meeus (2nd edition, Chapter 47). It is accurate to within about 0.3° for dates between 1900 and 2100, sufficient for rise/set time calculations to the nearest minute.

Why does moonrise shift by about 50 minutes each day?

The Moon orbits Earth eastward, completing one orbit in about 29.5 days. Each day the Moon moves roughly 13° eastward relative to the stars, so the Earth must rotate an extra ~50 minutes to bring the Moon back to the same altitude. This is why moonrise times are not fixed like solar times.

What does moon age mean?

Moon age is the number of days since the last new moon. A value of 0 means new moon, ~7 days is first quarter, ~14–15 days is full moon, and ~22 days is last quarter. The full lunar cycle (synodic month) averages 29.53 days.

What is the illuminated fraction?

The illuminated fraction is the percentage of the Moon's visible disk that is lit by the Sun. At new moon it is 0%, at full moon it is 100%, and at the quarters it is approximately 50%. The value is derived from the phase angle between the Moon, Earth, and Sun.

Why might moonrise or moonset show "None" for my location?

Near the poles, the Moon can remain above or below the horizon for multiple days, similar to the midnight sun phenomenon for the Sun. When the Moon does not rise or set on a given date at your latitude, the calculator reports "None" with an explanation.

How accurate are the times shown?

Times are accurate to within 1–2 minutes for most latitudes and dates. Precision decreases slightly near the Arctic or Antarctic circles and for dates far outside the 1900–2100 range. Atmospheric refraction uses the standard 0.5667° correction at the horizon.

Moonrise Moonset Calculator

Name: Moonrise Moonset Calculator
Availability: InStock
Author: Nham Vu

Calculate moonrise, moonset, lunar transit, moon phase, and illumination for any date and geographic location.

Location & Date

Latitude (°)

Longitude (°)

Date

UTC Offset (hours)

Enter location and date to calculate moon times

Summary

Calculate moonrise, moonset, lunar transit, moon phase, and illumination for any date and geographic location.

How it works

Enter your latitude and longitude, or click "Use My Location" to auto-fill from your browser.
Select the date you want to evaluate and enter your UTC offset.
The tool computes the Julian Day Number for the given date.
Lunar position (right ascension and declination) is calculated using Meeus low-precision orbital elements.
Rise and set times are determined by iterating the Moon's hour angle at the standard dip angle (0.833° + horizontal parallax).
The lunar phase angle and illuminated fraction are derived from the Moon's elongation from the Sun.

Use cases

Plan astrophotography sessions around a new moon for dark skies.
Find moonrise times for landscape photography with a full moon backdrop.
Schedule nighttime hiking or camping trips with adequate moonlight.
Track the lunar cycle for fishing, gardening, or tidal predictions.
Determine moon visibility for astronomical observations.
Calculate moon age and phase for religious or cultural calendar purposes.
Verify moonrise azimuth for alignment photography at specific landmarks.
Plan wildlife observation activities that depend on moon brightness.

Frequently Asked Questions

Related tools

Sun Position Calculator Julian Day Converter Sidereal Time Calculator

Last updated: 2026-05-29 · Reviewed by Nham Vu