Understanding the 8 Phases of the Moon
Here’s a “crash course” on understanding Moon phases.
Moon Phases at a Glance
- Full cycle: 29.53 days from New Moon to New Moon (a synodic month).
- Eight named phases: New, Waxing Crescent, First Quarter, Waxing Gibbous, Full, Waning Gibbous, Last Quarter, Waning Crescent.
- The two words to remember: waxing = growing in illumination; waning = shrinking.
- The trick to tell at a glance: in the Northern Hemisphere, if the right side of the Moon is lit, it’s waxing (growing); if the left side is lit, it’s waning (shrinking). Reverse this in the Southern Hemisphere.
- Why we see phases at all: we see whatever fraction of the Moon’s sunlit half is angled toward Earth at the moment.
How much do you know about Moon phases? Do you know which phase is invisible to us? Or what the difference is between waxing and waning? Here’s a crash course on understanding Moon phases.
According to the Encyclopaedia Britannica, lunar phases are not caused by Earth’s shadow (a common misconception) but by our changing viewing angle on the Moon’s sunlit hemisphere as the Moon orbits Earth. Earth’s shadow falls on the Moon only during the rarer event of a lunar eclipse, not during the regular monthly cycle.
Understanding Moon Phases and the Lunar Cycle
First, the Moon is on a 30-day cycle when it makes its orbit around the Earth. Actually, the entire trip takes 29.53 days, to be exact, and is measured from one “New Moon” to the next.
The Phases of the Moon
Here, we’ll break down each of the 8 phases of the Moon as it revolves around the Earth. Refer to the corresponding numbered phases in the diagram above in this article to follow along.
- New Moon. When we are in the “New” Moon phase, the Moon is not visible from our perspective because it is positioned between the Sun and Earth. The portion of the Moon that is actually getting sunlight is the back side of the Moon, the half that we cannot see. It’s called the New Moon because it’s the beginning of the lunar cycle. Push the “reset button” and let the 30-day orbit begin.
- Waxing Crescent. After the New Moon, the Moon continues its journey around the Earth, becoming visible as it moves on its path toward becoming a Full Moon. The sunlit portion is increasing. A crescent Moon is easy to identify as it looks like a sliver in the sky. Waxing = growing in illumination.
- First Quarter Moon. This one confuses a lot of people. In this case, the term is used because the Moon is in the first quarter of the 30-day cycle, but it appears half full. The First Quarter and Last Quarter Moons (both called “half moons”) happen when the Moon is at a 90 degree angle with respect to the Earth and Sun. So we are seeing exactly the half of the moon that gets hit by the Sun’s light.
- Waxing Gibbous. Still growing as we head toward full. More than half of the Moon is illuminated by the Sun. Gibbous = more than half. Waxing = growing in illumination.
- Full Moon. The full Moon comes about 15 days (14.8 to be exact) after the New Moon, the mid-point of the cycle (half of 30 = 15). The Moon is now in alignment with the Earth and Sun again, just as in the New Moon phase, but this time, the Moon is on the opposite side of Earth, so the entire portion of the Moon that is lit by the Sun is facing us. After this phase, which lasts only an instant, visibility starts decreasing.
- Waning Gibbous. Waning = decreasing in illumination as we head toward the darkness of the next New Moon. Gibbous = more than half.
- Last Quarter Moon (sometimes called the Third Quarter Moon). This is when the Moon completes the third quadrant of its phase cycle, about 22.1 days after the New Moon phase. And, as in #3, it looks like a half Moon to us again, except this time, it’s heading toward the New Moon phase (disappearing) instead of growing toward the full Moon phase.
- Waning Crescent. The Moon is a little sliver of a crescent, just as in #2, but the illuminated part is decreasing. Waning = decreasing in illumination. Now, the illuminated crescent is facing the opposite direction as when it was a waxing crescent (see #2).
The 8 Moon Phases by Day Count
| Phase | Day in cycle | What you see | Best for |
|---|---|---|---|
| New Moon | 0 | Nothing (Moon between Sun and Earth) | Deep-sky stargazing |
| Waxing Crescent | ~3 | Thin right-side sliver, west after sunset | Earthshine on the dark limb |
| First Quarter | ~7 | Right half lit, high in the south at sunset | Crater shadows along the terminator |
| Waxing Gibbous | ~10-13 | More than half lit, growing | Wide-field photography |
| Full Moon | ~15 | Fully lit, rises at sunset | Moonlit walks; tough for stargazing |
| Waning Gibbous | ~18 | More than half lit, shrinking, rises later | Late-night moonrise photography |
| Last Quarter | ~22 | Left half lit, rises around midnight | Predawn stargazing windows |
| Waning Crescent | ~26-28 | Thin left-side sliver, east before sunrise | Earthshine again, before sunrise |
Two terms to memorize:
Waxing = Growing in illumination
Waning = Shrinking in illumination
How Can You Tell if The Moon Is Waxing Or Waning?
If you look in the sky and see a crescent or gibbous Moon, here’s how to tell if it is in the waxing or waning phase by the direction it’s curving.
The simple shortcut in the Northern Hemisphere: if the right side of the Moon is lit (like the bowl of a “D”), the Moon is waxing toward Full. If the left side of the Moon is lit (like the bowl of a “C”), it is waning toward New. Memorize “D for darkening growing, C for completing the cycle,” and you’ll never get them mixed up. Southern-Hemisphere viewers see this exactly backwards.
Will the Next Phase Be Clear Overhead?
A New Moon for deep-sky viewing, a Full Moon for a walk: both depend on a clear sky. See your region’s long-range outlook.
See Your Extended ForecastSo there you have it. We’re happy to answer any questions to help you understand the fascinating changes in Earth’s satellite. Just leave them in the comments below.
Check out our Moon Phases Chart so you can see each phase, day by day, for the entire month.
Frequently Asked Questions About Moon Phases
How long does a full Moon cycle take?
29.53 days from one New Moon to the next, called a synodic month. The Moon itself orbits Earth a bit faster (27.32 days, a sidereal month), but because Earth has moved in its own orbit around the Sun in the meantime, the Moon needs an extra 2 days to “catch up” and re-align between Earth and Sun.
Why is the Moon invisible at New Moon?
Because the Moon is roughly between the Sun and Earth. The sunlit half of the Moon is pointed away from us; the half facing us is in shadow. The Moon is up in the daytime, lost in the Sun’s glare.
What’s the difference between waxing and waning?
Waxing means the illuminated portion is growing (New Moon to Full Moon). Waning means the illuminated portion is shrinking (Full Moon to New Moon). Quick mnemonic: waxing rhymes with “growing in”; waning rhymes with “fading.”
Why is a half Moon called a quarter Moon?
Because it marks the first or third quarter point of the 29.5-day lunar cycle, not because it looks like a quarter. Visually it looks like half a Moon because we are viewing one half of the sunlit hemisphere at a 90-degree angle.
How do you tell waxing from waning in a glance?
In the Northern Hemisphere, if the right side of the Moon is lit (looking like the bowl of a “D”), it is waxing toward Full. If the left side is lit (looking like a “C”), it is waning toward New. In the Southern Hemisphere this is reversed.
What’s a Gibbous Moon?
Any phase between Quarter and Full where more than half of the disc is lit. It looks like a slightly squashed full Moon. Waxing Gibbous comes between First Quarter and Full; Waning Gibbous comes between Full and Last Quarter.
What is “Earthshine”?
The faint glow on the darkened side of a thin crescent Moon. It’s reflected sunlight bouncing off Earth and back to the Moon, then back to us. It is best seen on Waxing Crescent (just after sunset) and Waning Crescent (just before sunrise).
For more moon reading, see supermoons explained, 9 moon myths from around the world, and the October Hunter’s Moon.
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This article was published by the Staff at FarmersAlmanac.com. Any questions? Contact us at questions@farmersalmananac.com.
- Farmers' Almanac Staff
- Farmers' Almanac Staff
- Farmers' Almanac Staff
- Farmers' Almanac Staff
Nice website
Northern hemisphere try:
Run a line throgh the crescent. It makes either a “P” or a “D”
Premiere is new, Dernier is last
Khadar
So should I take my cuttings of plants for propagation on the waxing gibbous moon?
On the dagram above, I think you meant to write that the moon’s orbit around the EARTH is not a circle.?
From what I have just read a new moon is seen every 30 day and the space between the new moons is 28 days? Meaning the new moon is both and ending And a beginning. Thanks for your reply
Very interesting piece on the moon. Now I’m a Moon maniac.
I am trying to understand what “lunar day” it is. If new moon Central time was March 2 @ 11:35 AM, then it would be the first lunar day until March 3 at moonrise, correct?
Then March 3rd, all day/night would be the 2nd lunar day from moonrise March 3 until moonrise on March 4? I am looking at two calendars online that state the lunar day and one of them is wrong. 🙂 thank you for any help.
When is the best time to prune?waning gibbious or waning crescent?
How does the moon phase make deer react