How to use the lunar calculator
The lunar calculator computes Moon position, phase and visibility for any date between 1900 and 2100. Use the fields on the left to set date, time, location and physical parameters. The result updates immediately on the right — current phase, equatorial and topocentric position, upcoming principal phases, Supermoons, eclipses and altitude curve for the next hours.
What this lunar calculator delivers
- Spotlight: phase, illumination, lunar age, distance (km + R⊕ + lunar diameters), magnitude, light time
- Phase 5+: Brown lunation, optical libration, bright limb angle, earthshine, orbital position
- Events: next 4+ principal phases, upcoming Supermoons and Micromoons, upcoming lunar and solar eclipses with visibility
- Altitude curve: SVG of the next N hours with horizon and pulsing "now" point
- Position: J2000 equatorial RA/Dec, topocentric (alt/az/hour angle/refraction), ecliptic longitude
- Sun and Time: solar position, JD UTC/TT scales, ΔT, local sidereal time, local events (moon and sun rise/transit/set)
- Geometry: elongation, phase angle, synodic fraction, geocentric and topocentric distance in km/R⊕, horizontal parallax, anomalistic orbit with Super/Micro classification
- Orientation: colongitude, libration lat/lon, subsolar lat/lon, tracking rates
- JSON payload: raw engine output for technical inspection
About the accuracy
The OCSE-Lite engine implements: truncated ELP-2000/82B (60 longitude terms + 60 latitude + 46 distance for the Moon, ~3 arcsec in lunar position), truncated VSOP87D (58 terms for heliocentric Earth, ~13 arcsec in the Sun), low-order IAU nutation, annual aberration, topocentric parallax, Bennett refraction, Espenak-Meeus ΔT (4000 BC — 3000 AD), exact Easter computus and equinoxes/solstices accurate to the minute. For amateur use, education, astrophotography and naked-eye observation — sufficient. For mission-critical aerospace, use NASA SPICE.
This lunar calculator is free, no signup, no data collection, runs entirely on the server — no paid external APIs, no heavy JS, no dependencies. Original code reproducible from public formulas in Meeus 1998, Astronomical Algorithms, 2nd ed.
Guide to input fields and results
This lunar calculator lets you configure physical and observational parameters to reproduce the Moon's position and geometry on any date. Below, what each field means.
Inputs — Time and location
- Date and Time: base instant of the calculation (in the time zone given under "IANA Time zone"). Default: now, in your local time zone.
- Latitude / Longitude: observer coordinates in decimal degrees. Negative in the Southern / Western hemispheres.
- Altitude (m): observer altitude above sea level. Marginally affects parallax and refraction.
- IANA Time zone: standard identifier (e.g.,
America/New_York,UTC). Determines how the entered time is converted to UTC.
Inputs — Atmospheric refraction
- Apply refraction: "Yes" uses Bennett's formula to correct the apparent altitude of the Moon and Sun near the horizon; "No" shows pure geometric altitude. Pressure (1013 hPa), temperature (15 °C) and humidity (50%) use defaults adequate at sea level.
Inputs — Personal & presentation
- Your birth date: optional. When provided, the "Your lunar journey" card shows how many lunations you have lived and when the next New Moon is.
- Hemisphere (seasons): "Auto" deduces from latitude. Determines how the seasons card shows summer/winter.
- Calendar system: Gregorian is current; Julian is useful for historical dates before 1582.
- Result language: English, Portuguese or Spanish (affects phase names and folklore).
Inputs — Search horizons
- Eclipses (years) and Apsides (months): how far ahead the engine should search for lunar/solar eclipses and perigees/apogees.
- Super/Micro Moons (months): time window to detect Full Moons coinciding with perigee (Super) or apogee (Micro).
- Upcoming phases (count): how many principal phases (New, Waxing, Full, Waning) to list.
- Altitude curve (h and min): hours ahead plotted on the SVG and sampling step in minutes.
Outputs — Spotlight (highlight card)
- Illumination (%): percent of the visible face that is lit.
k = (1 + cos i)/2, where i is the phase angle. 0% New, 100% Full. - Lunar age (d): days elapsed since the last New Moon. Synodic cycle = 29.53 days.
- Distance: topocentric (from the observer) in km, Earth radii (R⊕) and multiples of the lunar diameter (∅L = 3,474.8 km).
- Apparent diameter: Moon's angular size in arcmin. Larger at Supermoon, smaller at Micromoon.
- Apparent magnitude: estimated visual brightness. Full Moon ≈ −12.7. Computed via Allen 1976.
- Light time: seconds it takes a photon to travel Moon → Earth. ~1.28s on average.
Outputs — Phase 5/6/7 (cards)
- Brown lunation: sequential number of the current synodic cycle counted from the New Moon of 1923-01-17 (lunation #1).
- Optical libration: angular offset in longitude and latitude that makes ~59% of the Moon visible across each month.
- Bright limb angle: direction of the illuminated limb on the celestial sphere, measured from celestial north in degrees.
- Earthshine: intensity of light reflected by the Earth onto the Moon's dark side ("Da Vinci glow"). Visible only near New Moon.
- Orbital position: percentage along the perigee→apogee cycle (0% perigee, 100% apogee).
Outputs — Equatorial and topocentric position
- RA (Right Ascension): equatorial coordinate analogous to celestial longitude, in hours:minutes:seconds (HMS) or degrees.
- Dec (Declination): equatorial coordinate analogous to celestial latitude, in degrees DD:MM:SS.
- Ecliptic longitude λ: coordinate on the ecliptic, base of lunar computations.
- Ecliptic latitude β: Moon's offset relative to the ecliptic.
- Geometric/apparent altitude: height above the horizon without/with atmospheric refraction.
- Azimuth: horizontal direction measured from North (0°), East (90°), South (180°), West (270°).
- Hour angle: angle between the local meridian and the object. Positive west of the meridian.
Outputs — Local events and time scales
- Moonrise/transit/moonset: local times of horizon crossing and culmination.
- Sunrise/sunset: same events for the Sun (reference).
- JD UTC / JD TT: Julian Day in UTC (Coordinated Universal Time) and TT (Terrestrial Time, used for coordinates).
- Local Sidereal Time: local sidereal hour in degrees or HMS. Defines which right ascension culminates now.
- ΔT (s): effective TT−UT1 difference applied in the calculation.
Export and reproduce
The 3 buttons at the top of the result let you download the computed instant as CSV (50+ key-value-unit rows), JSON (raw engine output) or copy directly to the clipboard. Useful in spreadsheets, scripts or citations in academic work. The filename already includes date and location.
Frequently asked questions
How does the lunar calculator work?
You provide date, time and location. The lunar calculator uses the OCSE-Lite engine with truncated ELP-2000/82B series (60+ terms for the Moon, Chapront-Touzé 1988) and VSOP87D (50+ terms for the Sun, Bretagnon 1988), with typical accuracy of ~3″ in lunar position. It computes phase, equatorial position, topocentric coordinates, libration, upcoming eclipses and Supermoons.
What is the accuracy of the lunar calculator?
In standard mode (engine_mode=auto), lunar position ~5″ RSS (truncated ELP-2000/82B). In de440 mode with SOFA polyfill enabled, ~0.005″ (~5 mas) using the DE440 kernel (Park et al. 2021, NASA/JPL) with IAU 2000A nutation and IAU 2006 P03 precession. Distance <1 km (de440), <50 km (lite). Phase times ±30s (lite) or ±5s (de440). Eclipses: magnitude ~0.5% canonical with Besselian elements + DE440 + light-time correction. Equinoxes and Easter exact to the minute. For academic use or paper citation, see the scientific version + methodology. For mission-critical aerospace, use NASA SPICE.
What does each output field mean?
Illumination: percent of the visible face that is lit. Age: days since the last New Moon. RA/Dec: J2000 equatorial position. Az/Alt: altitude above the local horizon. Libration: effective visible face of the Moon. Magnitude: apparent visual brightness. Next eclipse: date, magnitude, visibility from your region.
Can I query any date?
Yes, any date between 4000 BC and 3000 AD with Espenak-Meeus ΔT (accuracy degrades at the extremes). Ideal window 1900-2100.
Does the lunar calculator work for other countries?
Yes. Under "Observer location" you can change latitude, longitude and altitude to any point on the globe, or pick a city from the selector. Times default to your selected time zone.
How do I export the results?
Use the buttons at the top of the result: "Copy link" puts the full URL (with all parameters) on the clipboard; "Print" opens the print dialog; "Download JSON" saves the full computation (engine + derived values + upcoming events) as pretty-printed JSON. There is also CSV for spreadsheets and direct copy of the engine payload.
What are Supermoons and Micromoons?
A Supermoon is a Full Moon coinciding with perigee (~360,000 km from Earth) — it appears ~14% larger and ~30% brighter than a Micromoon, which is a Full Moon coinciding with apogee (~405,000 km). The calculator lists upcoming ones for the next 24 months.
What is lunar libration?
Optical libration is the apparent "rocking" of the Moon that lets us see up to 59% of the surface across each lunation (without libration we would see only 50%). The calculator shows libration in longitude (±7.9°) and latitude (±6.7°) computed by Meeus theory.
Can I use this for astrophotography?
Yes. The "Best time to photograph the Moon today" section computes the lunar golden hour (Moon near horizon), landscape window with Moon, best close-up (near transit — less atmospheric extinction) and the worst window (Moon almost on the horizon). Combine with the altitude curve and twilight bands for full planning.
Is the data free to reuse?
Yes. Computation derives from Meeus 1998 (public algorithms) — you can cite freely in school work, blogs, posts. For formal academic citation, prefer the scientific version + methodology page with peer-reviewed references.