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Glossary Science & Engineering

Moon phase

A moon phase is how much of the Moon's sunlit face is visible from Earth, cycling from new moon to full moon and back about every 29.5 days.

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In more detail

The cycle is called the synodic month. The Moon is full when it is opposite the Sun in the sky and new when it is in the same direction as the Sun. Tides are largest around new and full moons.

Try these tools

Moon Phase Calculator

Find the Moon's phase, percentage illuminated and age for any date and time, with a picture of the Moon and the dates of the next new moon.

See also

  • Glossary Sunrise and sunset
    Sunrise and sunset are the times the top edge of the Sun crosses the horizon, which depend on date and latitude.
  • Glossary Dew point
    The dew point is the temperature to which air must cool for water vapour to condense into dew; the higher it is, the muggier the air feels.
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