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| Moon Phases on Jul 26, 2012

Understanding first quarter moon

A first quarter moon rises at noon and is high overhead at sunset. It sets around midnight.

A first quarter moon shows half of its lighted hemisphere – half of its day side – to Earth.

But we officially call this moon a quarter and not a half because it is one quarter of the way around in its orbit of Earth, as measured from one new moon to the next.

First quarter moon from Muscat, Oman via EarthSky Facebook friend Priya Kumar. Beautiful Priya!

This moon appears half-lit to us, and half moon is a beloved name (although not an official one). Still, it’s good to recall that the illuminated portion of a first quarter moon truly is just a quarter. On the night of first quarter moon, we see half the moon’s day side, or a true quarter of the moon. Another lighted quarter of the moon shines just as brightly in the direction opposite Earth!

A first quarter moon rises at noon and is high overhead at sunset. It sets around midnight.

First quarter moon comes a week after new moon. Now, as seen from above, the moon in its orbit around Earth is at right angles to a line between the Earth and sun.

As the moon orbits Earth, it changes phase in an orderly way. Follow these links to understand the various phases of the moon.

Understanding Moon Phases
Waxing Crescent
First Quarter
Waxing Gibbous
Full Moon
Waning Gibbous
Last Quarter
Waning Crescent
New Moon