What did the Moon look like on your birthday?
A birthday is a date on a calendar. The Moon keeps changing throughout it. Choose a local time and timezone to explore one instant, with no account, email or purchase required.
A birthday. A moment. One Moon.
When was your moment?
Choose a date and the local timezone. The place helps find that timezone and can carry the same moment into a star map. Global phase is the same at the same instant wherever you are.
No account, email or purchase needed. City lookup: GeoNames · CC BY 4.0. An unknown time uses a labelled 22:00 local-time assumption, not a whole-day average.
Calculated reference example
Budapest, a summer evening
17.8%illuminated · Waning crescent
21 June 2025 · 22:00 Europe/Budapest · 20:00 UTC
Waning crescent · 17.8% illuminated.
Phase longitude 310.31° · Sun–Moon–Earth angle 130.09°.
A geocentric phase diagram: waxing light on the right, waning on the left. Your local view can be rotated, below the horizon or hidden by daylight and clouds. This is not a lunar-surface photograph or a prediction of visibility.
Calculate a moment to carry it privately into the star-map designer. A saved design stays yours until you choose otherwise.
Explore the whole sky ↗Read the light
One cycle, eight familiar names.
These simplified reference diagrams mark eighths of the cycle. The principal phases are exact instants; the calculator names the nearest eighth and reports the actual numerical values. A name such as “Full Moon” does not mean precisely 100% illumination throughout a day.
- New Moon0° Phase longitude
- Waxing crescent45° Phase longitude
- First quarter90° Phase longitude
- Waxing gibbous135° Phase longitude
- Full Moon180° Phase longitude
- Waning gibbous225° Phase longitude
- Last quarter270° Phase longitude
- Waning crescent315° Phase longitude
Waxing means moving toward full; waning means moving toward new. Phase longitude runs from 0° at new, through 90° at first quarter and 180° at full, to 270° at last quarter. The separate Sun–Moon–Earth angle measures illumination geometry and runs the other way: near 180° at new and near 0° at full.
Begin with the date, then the time
Use the date and local time at the place where the moment happened, not the time shown on your device today. Search for a city to find its coordinates and IANA timezone, or enter coordinates yourself. The place label can be your own wording; the timezone needs to describe the actual clock. If you do not know the time, untick the time box. The calculator then uses 22:00 local time and labels that assumption. It is one example during the date, not a recovered birth time or an average for the whole day.
One phase for the same instant
The result is geocentric: phase and illumination are calculated from Earth’s centre. People in different countries share the same global phase at the same instant, although their calendars and clocks may show different dates. The place is useful for resolving local time and for a later star map; it does not choose a different global Moon phase. Clocks changing for daylight saving can create a missing or repeated local time. The calculator rejects a missing time and asks which occurrence you mean when it happens twice.
Read the two angles
Phase longitude measures the Moon’s progress relative to the Sun along the ecliptic: 0° at new, 90° at first quarter, 180° at full and 270° at last quarter. The separate Sun–Moon–Earth angle describes illumination geometry, approaching 180° at new and 0° at full. The illuminated fraction is calculated separately, rather than guessed from a phase icon. The eight familiar names describe the nearest eighth of the cycle; principal phases occur at exact instants. Near a boundary, a short time change can change the displayed name while the illumination changes smoothly.
The diagram has a viewing convention
Waxing light appears on the right in this schematic diagram and waning light on the left. Its illuminated area follows the calculated fraction. It is not an oriented photograph or a simulation of the Moon above your horizon: the apparent tilt depends on your place and the observation time. The diagram also does not show surface markings, libration, eclipses, cloud, daylight or whether the Moon was above the horizon. A dark Moon is not an empty calculation; it can be the correct result near new moon.
The calculation and an independent check
The local engine uses Skyfield with the pinned JPL DE440s ephemeris. Numerical checks compare phase events and illuminated fractions with independent US Naval Observatory reference values.
Independent fixed public reference fixtures cover principal phases in 1900/2000/2025/2100 and four rounded 2025 illumination values; this is finite numerical verification, not certification of every instant.
Read the original source ↗Source checked November 3, 2026 · Starmap Company editorial
What phase and illumination mean
Phase longitude and illuminated fraction describe different aspects of the same lunar cycle. The result reports both the chosen local time and its resolved UTC instant.
Skyfield’s primary documentation describes geocentric lunar phase calculations. The calculator’s fixed schematic orientation is disclosed separately.
Read the original source ↗Source checked November 3, 2026 · Starmap Company editorial
A moment, without a public birthday page
The calculator sends the entries in a private POST request and shows the result in this browser. It does not create a public date-and-city URL, share page or downloadable poster. If you want to explore a star map for the same moment, use the optional private handoff. A design already saved in the studio is kept until you choose whether to continue it or start another. This tool describes astronomy; it does not assign a personality, relationship outcome or astrological meaning to your birthday.
A little more about the Moon
Does the time change the Moon phase?
Yes. The phase changes continuously, and a date alone spans many hours. A known local time and the correct timezone identify one instant. Unknown time uses a clearly labelled 22:00 assumption; you can try another known time to compare.
Link to this answer: Does the time change the Moon phase?Why does my result differ from a calendar?
A calendar may show a principal phase rounded to a date in another timezone. This calculator uses the exact chosen instant and names the nearest eighth of the cycle. Compare UTC instants and numerical illumination before treating different words or dates as a disagreement.
Link to this answer: Why does my result differ from a calendar?Is this an astronomy calculation or an astrology reading?
Astronomy. It reports a calculated phase and illuminated fraction. It makes no personality, compatibility, health or fortune claim.
Link to this answer: Is this an astronomy calculation or an astrology reading?Will the diagram look tilted in the real sky?
It can. The diagram deliberately uses waxing-right and waning-left illumination. Local horizon orientation and visibility are different calculations and are not represented here.
Link to this answer: Will the diagram look tilted in the real sky?