Moon Phase Calculator

Find the current moon phase and moon illumination for any date.

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Moon Phase
First Quarter
Illumination: 50.8%

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Understanding Moon Phases

The moon phases are caused by the changing positions of the moon, Earth, and sun. As the moon orbits Earth, different portions of its sunlit surface become visible from our planet.

The Eight Phases

  • New Moon: The moon is between Earth and the sun; the dark side faces us.
  • Waxing Crescent: A small sliver of the right side becomes visible.
  • First Quarter: Half of the moon is illuminated.
  • Waxing Gibbous: More than half is lit; approaching full.
  • Full Moon: The entire face is illuminated.
  • Waning Gibbous: Light begins to decrease from the right.
  • Third Quarter: The left half is illuminated.
  • Waning Crescent: A small sliver remains on the left.

Frequently Asked Questions

It uses a simplified astronomical algorithm based on the known new moon of January 6, 2000. It calculates how many days have passed since that date and determines the current phase by dividing by the lunar cycle length of 29.53 days.

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