Moon Phase Calculator
Calculate Moon Phase
Formula
Moon age = (date − Jan 6, 2000) mod 29.53 days | Illumination ≈ (1 − cos(2π × age / 29.53)) / 2
Frequently Asked Questions
What is a synodic month?
A synodic month (about 29.53 days) is the time between two consecutive new moons. It represents one complete cycle of moon phases as seen from Earth.
How accurate is this moon phase calculator?
This calculator uses the average synodic month of 29.53 days from a known new moon reference date (January 6, 2000). It is accurate to within about 1 day for dates within a few decades of the reference.
What causes moon phases?
Moon phases are caused by the changing angle between the Sun, Earth, and Moon as the Moon orbits Earth. We see different amounts of the Moon's illuminated half depending on this angle.
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