What is a “First Quarter” Moon?

26 June 2014 
The Short Answer (TSA)

            The “1st Quarter” is one of the major phases of the Moon in which half of the face of the Moon is sunlit. In the Northern Hemisphere, the right half of the Moon is sunlit at the “1st Quarter.” It’s just the opposite in the Southern Hemisphere with the left half of the Moon sunlit at the 1st Quarter.”

1st Quarter Moon (Northern Hemisphere)

The “1st Quarter” Moon is increasing in size — “waxing.”  After the “1st Quarter,” the sunlit half of the Moon’s face continues to increase in size until it reaches the next major phase, the “Full Moon.”  At the Full Moon, the whole face of the Moon is sunlit.

The “quarter” part of the “1st Quarter” phase name, sometimes, causes confusion.  If half the face of the Moon is sunlit, why is it called a “quarter” instead of a “half?”  Because the term “quarter” refers to time – not the sunlit part of the face of the Moon.  So, the “1st Quarter” is one quarter (1/4th) of the way through the full cycle of the Moon’s phases.

The major phases begin with the “New Moon” – the Moon disappears from the sky. Then, the Moon reappears increasing in size (waxing) until it reaches the halfway point – the “1st Quarter.”

After the “1st Quarter” phase, the sunlit part of the face of the Moon continues to increase (wax) until the Moon’s “full” face is sunlit – the “Full Moon” phase.

Then, after the Full Moon, the sunlit part of the Moon’s face begins to “wane” or decrease in size until, again, only half of the face of the Moon is sunlit.  That’s the next major phase, the “3rd Quarter” Moon.  The 1st and 3rd Quarter Moons look just a little different.  If you live in the Northern Hemisphere, the right side of the Moon’s face is sunlit at the 1st Quarter.  At the “3rd Quarter,” the other side — the left side of the Moon’s face is sunlit.

What is you live in the Southern Hemisphere?  The left-right rule is exactly the opposite.  The left half of the 1st Quarter Moon is sunlit, while the right half of the 3rd Quarter Moon is sunlit.

1st Quarter Moon (Southern Hemisphere)

After the “3rd Quarter” phase, the sunlit part of the Moon’s face continues to decrease in size (wane) until the Moon’s face disappears from the night sky.  When the Moon’s face disappears, the “New Moon” phase has come.  And, with the New Moon, a new cycle of the Moon’s phases begins.

The, so called, major phases are the “New Moon” (no Moon), “1st Quarter” (half Moon), “Full Moon” (whole Moon), and “3rd Quarter” (half Moon, again). After the 3rd Quarter the cycle starts over with the new Moon.

 The Moon's Phases

M Grossmann of Hazelwood, Missouri
(& Belleville, Illinois)
About the Author

26 June 2014