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Moon Phase Calculator

Find the moon phase, illumination and lunar age for any date and hemisphere.

Related tools

All Astronomy tools →
Star Visibility CalculatorEstimate how many stars you can see from light pollution, moon phase, clouds and humidity.Sun Position CalculatorCompute the sun's azimuth and elevation for any location, date and time.Sunrise & Sunset CalculatorFind sunrise, sunset, solar noon and day length for any location and date.Tide Time CalculatorEstimate the day's high and low tide times from a known reference tide and pattern.Surface gravity calculatorCompute the surface gravity of a planet or moon from its mass and radius.

Open Moon Phase Calculator and you get an answer straight away, with no account to create. You will find it under Astronomy, with Star Visibility Calculator and Sun Position Calculator for the neighbouring cases.

How to use it

  1. Open the tool — no signup or install needed.
  2. Enter your input or adjust the available options.
  3. Get your result instantly, then copy or download it.

Frequently asked questions

What is Moon Phase Calculator?

Find the moon phase, illumination and lunar age for any date and hemisphere.

When would I actually use this?

Planning an observation or a photograph: when the sun sets, what phase the moon is in, and when an equinox or a solstice actually falls this year.

What is the most common mistake?

Treating the equinox as a fixed calendar date. It drifts by up to two days because the tropical year is not a whole number of days, which is the same reason leap years exist.

How is Moon Phase Calculator different from Star Visibility Calculator?

They sit next to each other but answer different questions. Star Visibility Calculator: estimate how many stars you can see from light pollution, moon phase, clouds and humidity. Pick whichever matches what you're starting from — both are free.

Is there a tool for the next step?

Sun Position Calculator is the closest one after this: Compute the sun's azimuth and elevation for any location, date and time.

What else is worth having open alongside it?

Sunrise & Sunset Calculator and Tide Time Calculator — they come up in the same task often enough to be worth a second tab.

Where do the figures come from?

Positions are computed from published ephemeris algorithms (Meeus) including the correction for the Earth's irregular rotation, so results agree with an almanac to well under a minute for the coming decades.

Further reading

All guides →
ExplainerHow Moon Phases Work: Two Months, Eight Shapes, and No ShadowThe phase cycle takes 29.53 days but the orbit takes only 27.32, and the 2.21-day gap is the entire explanation. With the eight phases, their illumination, when each rises and sets, and how they flip south of the equator.How-toPredicting Tides From a Single Known High WaterOne high water and the 12 h 25 min lunar interval give you every high and low for days. The rule of twelfths then tells you how much water has moved at any point in between — and both stop being reliable at exactly the same place.ExplainerSolar Noon Is Not Twelve O'ClockSunrise, sunset and the moment the sun is highest all hang off your longitude, not off the clock on the wall. In the same legal time zone, solar noon can be an hour and three quarters apart — and that gap explains most surprises about when the sun comes up.ExplainerThe Golden Hour and the Blue Hour Are Angles, Not HoursGolden hour runs from +6° to −4° of solar elevation and blue hour from −4° to −6°, which is why it lasts forty minutes at the equator, over an hour at mid-latitudes, and above 72.6° in June does not happen at all. The thresholds this calculator uses, checked against its own output.ExplainerThe Pendulum That Beats Seconds Is Not One Metre LongA one-metre pendulum swings in 2.0061 seconds, not 2. Getting to exactly two takes 0.994 m — and quadrupling the length only doubles the period.ComparisonWhich Fishing Knot Holds Best, and Why Every Published Table DisagreesKnot strength is quoted as a percentage of the line's rated breaking strain, and the percentages in circulation come from tests nobody agrees on. What the calculator on this page really stores, what one peer-reviewed measurement actually found, where a line breaks and why, and how to match a knot to its job.