Why does the moon seem to change its shape every night? It’s because the moon is a world in space, just as Earth is. Like Earth, the sun always illuminates half of the moon; the round globe of the moon has a day side and a night side. And, like Earth, the moon is always moving through space. So as seen from our earthly vantage point, as the moon orbits around Earth once each month, we see varying fractions of its day and night sides: the changing phases of the moon. How can you understand moon phases? Here are four things to remember.
1. When you see the moon, think of the whereabouts of the sun.
After all, it’s the sun that’s illuminating and creating the dayside of the moon.
The fact is, moon phases depend on where the moon is with respect to the sun in space.
But don’t just take our word for it. Go outside. No matter what phase of the moon you see in your sky, think about where the sun is. It’ll help you begin to understand why the moon you see is in that particular phase.
2. The moon rises in the east and sets in the west, every day.
It has to. The rising and setting of all celestial objects is due to Earth’s continuous daily spin beneath the sky.
So, when you see a thin crescent moon in the west after sunset, it’s not a rising moon. Instead, it’s a setting moon. In fact, it rose earlier in the morning soon after the sun rose.
3. The moon takes about a month to orbit the Earth.
Although the moon rises in the east and sets in the west each day (due to Earth’s spin), it’s also moving on the sky’s dome each day due to its own motion in orbit around Earth.
This is a slower, less noticeable motion of the moon. And it’s a motion in front of the fixed stars. So, if you just glance at the moon one evening – and see it again a few hours later – you’ll notice it has moved westward. In fact, that westward motion is caused by Earth’s spin.
By the way, the moon’s own orbital motion can be detected in the course of a single night. But you have to watch the moon closely, with respect to stars in its vicinity, over several hours.
Additionally, the moon’s eastward, orbital motion is easy to notice from one day (or night) to the next. It’s as though the moon is moving on the inside of a circle of 360 degrees. The moon’s orbit carries it around Earth’s sky once a month, because the moon takes about a month to orbit Earth.
So, the moon moves – with respect to the fixed stars – by about 12 to 13 degrees each day.
4. The moon’s orbital motion is toward the east.
Each day, the moon moves another 12 to 13 degrees toward the east on the sky’s dome. Then, Earth’s rotation takes a little longer to bring you around to where the moon is in space.
Thus, the moon rises, on average, about 50 minutes later each day.
The later and later rising times of the moon cause our companion world to appear in a different part of the sky at each nightfall for the two weeks between new and full moon.
Then, in the two weeks after full moon, you’ll find the moon rising later and later at night.
More details on individual moon phases at the links below
Follow the links to learn more about the various phases of the moon.
New Moon Waxing Crescent First Quarter Waxing Gibbous Full Moon Waning Gibbous Last Quarter Waning Crescent
Plus, here are the names of all the full moons.
Visit Sunrise Sunset Calendars to make your custom moon phases, moonrise-moonset and sunrise-sunset calendar.
Bottom line: The moon is a world in space just as Earth is and half of it is always illuminated by the sun. As the moon orbits Earth, we on Earth’s surface see varying fractions of its lighted face, or day side. These are the changing phases of the moon. Four tips to understanding moon phases, here.
Deborah Byrd
View Articles
About the Author:
Deborah Byrd created the EarthSky radio series in 1991 and founded EarthSky.org in 1994. Prior to that, she had worked for the University of Texas McDonald Observatory since 1976, and created and produced their Star Date radio series. Today, she serves as Editor-in-Chief of this website. She has won a galaxy of awards from the broadcasting and science communities, including having an asteroid named 3505 Byrd in her honor. In 2020, she won the Education Prize from the American Astronomical Society, the largest organization of professional astronomers in North America. A science communicator and educator since 1976, Byrd believes in science as a force for good in the world and a vital tool for the 21st century. "Being an EarthSky editor is like hosting a big global party for cool nature-lovers," she says.
In common usage, the four major phases are the new moon, the first quarter, the full moon and the last quarter; the four minor phases are waxing crescent, waxing gibbous, waning gibbous, and waning crescent.
The eight lunar phases are, in order: new moon, waxing crescent, first quarter, waxing gibbous, full moon, waning gibbous, third quarter and waning crescent.
A moon phase is the shape of moon's sunlit portion as seen from Earth. There are a total of eight moon phases: new, waxing crescent, first quarter, waxing gibbous, full, waning gibbous, third quarter, and waning crescent. These phases repeat every 29.5 days.
That gives you the order of the waxing phases, then reverse it to get the waning phases: FGQCN. The good thing about this sequence of letters is that you just have to memorize it one way! During your Moon Phases quiz you can write it down and then reverse it.
There are eight total phases of the moon cycle, four primary and four secondary. The primary phases are the new moon, first quarter, full moon, and last quarter. The secondary phases are waxing crescent, waxing gibbous, waning crescent and waning gibbous.
🌑 New: We cannot see the Moon when it is a new moon. 🌒 Waxing Crescent: In the Northern Hemisphere, we see the waxing crescent phase as a thin crescent of light on the right. 🌓 First Quarter: We see the first quarter phase as a half moon. 🌔 Waxing Gibbous: The waxing gibbous phase is between a half moon and full moon.
These different shapes are called the phases of the Moon, and they change with a regular pattern over a period of about 30 days. The phases of the Moon are caused by the changing positions of the Moon, Earth, and the Sun. As the Moon goes around the Earth, different parts of it are illuminated by the Sun.
One quick way to tell if a moon is in a waxing or waning phase is which side of the moon is the shadow on. If the shadow is on the right, like it is today, we are in a waning phase. If the shadow is on the left, then we are waxing and heading towards a full moon.
There are eight phases of the Moon beginning with the new Moon, followed by waxing crescent, first quarter, waxing gibbous, full Moon, waning gibbous, third quarter and finally waning crescent. This cycle repeats once every 29.5 days.
The cycle of moon phases impacts us and Earth in various ways. While many interpret great meaning of the phases of the moon, as mentioned above in each phase, the moon also plays a role in tides and agriculture, as well as holds significant cultural significance in parts of the world.
The Moon doesn't emit (give off) light itself, the 'moonlight' we see is actually the Sun's light reflected off the lunar surface. So, as the Moon orbits the Earth, the Sun lights up different parts of it, making it seem as if the Moon is changing shape.
The Moon is a large natural object that orbits, or travels around, Earth. After the Sun it is the brightest object in the sky. The average distance between the Moon and Earth is about 238,900 miles (384,400 kilometers). Compared to the distance between other planets and Earth, this distance is small.
Technically, the phases New Moon, First Quarter, Full Moon, and Last Quarter are defined to occur when the excess of the apparent ecliptic (celestial) longitude of the Moon over that of the Sun is 0, 90, 180, and 270 degrees, respectively.
Use Visual Aids. In addition to the anchor chart, you can use other visual aids such as pictures, diagrams, and videos to help your students understand the moon phases. For example, you can show them a time-lapse video of the moon phases or a diagram of the moon's orbit around the Earth.
Waxing Gibbous: The Waxing Gibbous is the fourth phase in the cycle of phases. This Moon phase occurs once a month, rising around 3 pm, and setting around 3 am, sticking around for approximately 7.38 days before going into the Full Moon phase.
At New Moon the percent illuminated is 0; at First and Last Quarters it is 50%; and at Full Moon it is 100%. During the crescent phases the percent illuminated is between 0 and 50% and during gibbous phases it is between 50% and 100%.
Introduction: My name is Jonah Leffler, I am a determined, faithful, outstanding, inexpensive, cheerful, determined, smiling person who loves writing and wants to share my knowledge and understanding with you.
We notice you're using an ad blocker
Without advertising income, we can't keep making this site awesome for you.
