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When I really started paying attention to the Sun, stars and Moon many years ago, one of the things that confused me was why the Quarter Moons looked like Half Moons.

The Moon is at or near its last quarter phase tonight, February 6, and into tomorrow morning. (The precise time is tomorrow at 15:54.)  Take a look tonight and you will see half of the Moon. Half the moon always faces us, and half the moon is always lit by the sun, though we can’t see that. To astronomers, there are no ‘half moons.’

So why does this phase get the name Quarter Moon is we can see half of it lit?  First quarter moon means the moon is one-quarter of the way through the current orbital cycle. Tonight’s third or last quarter moon means the moon is three-quarters of the way through the cycle, as measured from one new moon to the next.

moon phases

The phases of the Moon as viewed looking southward from the Northern Hemisphere. Each phase would be rotated 180° if seen looking northward from the Southern Hemisphere. The upper part of the diagram is not to scale, as the Moon is much farther from Earth than shown here. Image: wikipedia.org

It is all about perspective. At first quarter moon, the near side of the moon (the part we see) is half-illuminated by sunlight and half in its own shadow, so we are seeing half the moon’s day side.

It may also seem curious that in the Southern Hemisphere tonight the right side is 50% lit and in my Northern Hemisphere it is the left side that is bright. Yes, when we enter the first quarter that will be reversed.

A third quarter moon always rises in the middle of the night. It will appear at its highest in the sky around dawn, and will set around midday.


To move away from the sky though, I do like the name “Half Moon.” Half Moon Bay is a town on the California coast that I visited once and the name seems kind of romantic. There is a song called “Half Moon Bay” from 1969 by a band that I followed, Mott the Hoople. The lyrics have nothing to do with the town and the Dylan-esque vocals don’t make the lyrics any happier or romantic. It was a song I liked for its Procol Harum-like organ back then – and the album’s Escher cover is still a favorite. (Listen  on YouTube)

Another more recent song with that same title is by Train.  This one is actually about the California town and more “romantic.”

This ain’t a threat but I think I better warn ya’
Gonna fall in love if you go to California
I did and this is how I know
By the beach north of San José
Met the right girl and it sounds cliché
But we decided not to take it slow

But remember, there may be a Half Moon Bay, but there are no half moons.

quarter-moon

Moon phases are measured in quarters. This month’s New Moon is on July 4 (nice darkness for fireworks) and the First Quarter is July 11, followed by the Full Moon on July 19 and the Third Quarter on July 26. That may seem a bit illogical in its order, and the names may seem off too because a quarter moon appears to us as a “half moon.”

The moon reaches its half-illuminated last quarter phase at the same instant worldwide, it occurs at different times by the clock, depending on one’s time zone.  A last quarter moon rises in the middle of the night and shines in the morning sky.

Although half-lit, it’s called a last quarter or third quarter moon because the moon is three-quarters of the way in its journey from new moon to new moon.

first-quarter-earth-may-29-2016

First Quarter Earth as it would be seen from space

Tonight the Moon will look like a “half-moon” but it is officially at the First Quarter. It will be 45 percent visible to us, which certainly sounds like about a half-moon. About half of it will be illuminated by direct sunlight, but it will be only “7 days old” in its waxing growth from the New Moon when its unilluminated side was facing the Earth. So, it is a quarter of the way into its cycle of phases from new to full.

moon 4 phases

Quick Review

The Waxing (“increasing”)  crescent is when the Moon appears to be partly but less than one-half illuminated by direct sunlight.

First Quarter is when it looks like half a circle because it has completed one-quarter of an orbit around the Earth from either the full or new position.

Waxing Gibbous is when it appears to be more than one-half but not fully illuminated by direct sunlight.

The most popular phase, the Full Moon, is when the entire illuminated side is facing the Earth.

And then as we see less of it from Earth, the Waning Gibbous appears to be more than one-half but not fully illuminated by direct sunlight.

The Last Quarter is that other half of the Moon being illuminated by direct sunlight, and the Waning Crescent is the other side of the Waxing Crescent.

A nice site to see all the phases on a calendar is MoonGiant.com

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