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Last quarter moon at March equinox

A last quarter moon rises around midnight. It appears half illuminated from Earth. This month’s falls on the March 2017 equinox.

The last quarter moon was near Saturn on the morning of the March equinox (March 20, 2017). Photo via our friend Lunar 101 – Moon Book.

Last quarter moon comes on March 20, 2017 at 15:58 UTC. (Translate to your time zone here). That’s the day of the 2017 vernal equinox.

A last quarter moon looks half-illuminated. It rises around midnight, appears at its highest in the sky at dawn, and sets around noon. Fun time to see a last quarter moon: just after it rises, shortly after midnight. Then the lighted portion points downward, to the sun below your feet. Great time to think of yourself in the three-dimensional world of outer space!

Last quarter moon comes about three weeks after the previous new moon and about a week before the next new moon. New moon will come on March 28, 2017 at 02:57 UTC; translate to your time zone.

At the last quarter phase, as seen from above, the moon in its orbit around Earth is at right angles to a line between the Earth and sun. The moon is now three-quarters of the way around in its orbit of Earth, as measured from one new moon to the next.

After the last quarter phase, the moon begins edging noticeably closer to the sun again on the sky’s dome. Fewer people notice the moon during the day from about last quarter on, because the sun’s glare begins to drown the moon from view.

A last quarter moon can be used as a guidepost to Earth’s direction of motion in orbit around the sun. In other words, when you look at a last quarter moon high in the predawn sky, you’re gazing out approximately along the path of Earth’s orbit, in a forward direction. The moon is moving in orbit around the sun with the Earth. But, if we could somehow anchor the moon in space . . . tie it down, keep it still . . . Earth’s orbital speed of 18 miles per second would carry us across the space between us and the moon in only a few hours.

All you need to know: 2017 March equinox

Nearly a last quarter moon as seen from Sabah, North Borneo on the morning of March 20, 2017. Can you see that the lunar terminator – or line between light and dark – is a bit convex? This is the line of sunset on the moon. As the moon moved in its orbit around Earth throughout the day on March 20 – and as Earth spun under the sky – the line straightened as seen from Earth. The moon reaches its exact last quarter phase at at 15:58 UTC on March 20, 2017. Translate to your time zone here

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

Four keys to understanding moon phases

Where’s the moon? Waxing crescent
Where’s the moon? First quarter
Where’s the moon? Waxing gibbous
What’s special about a full moon?
Where’s the moon? Waning gibbous
Where’s the moon? Last quarter
Where’s the moon? Waning crescent
Where’s the moon? New phase

Moon in 2017: Phases, cycles, eclipses, supermoons and more

Deborah Byrd