What is a Full Moon?

Mary McMahon

When the Moon appears perfectly round in the sky, it is known as a “full moon,” indicating that the disc of the Moon is full or complete. This happen on average every 29 days, and advances in astronomy have allowed scientists to carefully predict their patterns. Many traditions and superstitions are associated with the full moon in almost every culture on Earth, especially when the moon becomes eclipsed, as will happen periodically.

The moon and earth.
The moon and earth.

The Moon appears to change shape because its orbit around the Earth, and through the Earth's orbit around the Sun. As the Moon moves behind the Earth, so that the planet is between it and the sun, more and more of the Moon will appear illuminated in a cycle called "waxing." When the Moon is all the way behind the Earth, the Sun's light will completely illuminate the visible side of the moon, making it look like a large, white disc in the sky. As the Moon moves around to the front of the Earth again, the visible disc shrinks, in a process referred to as "waning," until the it appears totally dark because the illuminated portion faces away from Earth.

The phases of the Moon progress from a new Moon, which appears as a thin crescent, to a full Moon.
The phases of the Moon progress from a new Moon, which appears as a thin crescent, to a full Moon.

Although the Moon generally takes a little over 27 days to completely orbit the Earth, it takes another few days for the Earth, moon, and sun to be in the proper alignment to create a full moon. As a result, the lunar cycle takes around 29 days in total. Since this cycle is such a present and obvious part of life, it lent its name to the word "month," which is derived from "moon."

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A full moon.
A full moon.

Occasionally, two full moons will appear in the same calendar month. The second is known as a "blue moon," and it is relatively uncommon. Some people consider blue moons to be highly auspicious, because of their rarity. More rarely, the month of February will have no full moon, since it is usually only 28 days long. When this happens, January or March will be marked with a blue moon. The Moon is also periodically eclipsed, thanks to its position behind the Earth. When the three planetary bodies reach the perfect alignment, the Earth's shadow will cover the Moon partially or totally.

The appearance of the Moon from Earth is referred to as a "lunar phase," reflecting the cyclical nature of the moon's appearance. Many cultures have historically tracked lunar phases, and associated certain superstitions and beliefs to them. The new moon, for example, is often linked with crime and questionable activity, since the night is dark, allowing people to participate in activities without detection. The full moon, on the other hand, has been associated with insanity, although studies have suggested that the Moon does not have influence on human or animal behavior.

A full moon occurs every 29 days.
A full moon occurs every 29 days.

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Discussion Comments


@Mykol – That sounds like a fun full moon ritual. I guess you really wouldn't need to string lights out in the yard for a cookout on such a bright night, because everyone would be able to see each other fairly well.

I have something that I do every time there is a full moon. I take a drive on this nearby highway that borders the coast. I roll the windows down and take in the ocean breeze.

I stop at my favorite beach and get out to watch the moonlight reflecting on the waves. It is truly beautiful.


@golf07 – I have noticed that dogs act differently when there is a full moon out. For one thing, they tend to bark a lot more.

Maybe it's because they can see further in the bright light. However, they can see pretty well at night without the moon, so it must be something more.

The coyotes out in the woods howl a lot when there is a full moon. This gets every dog in the neighborhood howling. So, I don't get much sleep on nights with a full moon.


Full moons are freakishly bright. I've often said that they are like giant natural streetlights, because they illuminate the world about as much as one streetlight would illuminate a yard.

I love sitting outside on a night with a full moon. It makes everything look blue. It gives me a neat perspective on what the world would look like if everything were the same color.


@anon160420 – The reason that the Earth doesn't block the sunlight from the moon is that the moon's orbit is offset from that of the Earth around the sun. So, light can get on through to the moon.

When lunar and solar eclipses occur, this is because the orbits have lined up perfectly. So, the light is blocked out then.


This article states that studies have shown that a full moon doesn't really affect human behavior, but I think my son would disagree with that statement.

He works in the psychiatric ward of a hospital and many times the staff will make a comment about it being a full moon because the patients are exhibiting such strange behavior.

I have also heard people say the emergency rooms at hospitals are often crazier than normal if there is a full moon.

It seems to happen often enough that it makes you wonder if a full moon really does have some kind of effect on human behavior.


I don't pay that much attention to the cycle of the moon, but still see when a full moon is because it is written down on almost every calendar I have.

I had never thought about the fact that the month of February doesn't have a full moon because it is such a short month. I think I will start paying closer attention to this, and see if I can identify the blue moon in January or March next time this rolls around.


We have some friends who live in the country and have a full moon party every month. It doesn't matter what day of the week this falls on, all of their friends and neighbors know they will have a party on that particular day. If someone enjoys throwing parties, a full moon party is as good excuse as any.

It is a good time to get together with good food and good conversation. They have done this so long that most people don't actually pay that much attention to what the moon looks like.

There are some nights though when it is hard to ignore because it is such a bright spot in the sky.


But won't the earth's shadow block the light from the sun?


for ocicats, 40 years ago, man walked on the moon.


I was asked when the last whole or complete Full Moon was...the hint was '40 years is a long time'.


Your welcome! All the Full Moons listed for 2008 are from Algonquin/Colonial. There are different names for different cultures such as, English/Medieval, Neo-pagan, Celtic. For example, Harvest Moon has other names such as Corn Moon, Fruit Moon, Nut Moon, Barley Moon, Blood Moon.


*Thanks* for posting the names of all the full moons. Your post said "for 2008"...do they change each year? Do the names change, or do they change which month they correspond with? I knew about blue moons, but have always been fascinated with the old names of each moon/month, would love to know where they originated. If you have a suggested reference, I would like to know it.


Full Moon names for 2008. Jan. Full Wolf Moon. Feb, Full Snow Moon. Mar, Full Worm Moon. Apr, Full Pink Moon. May Full Flower Moon. Jun, Full Strawberry Moon. July Full Buck Moon. Aug, Full Sturgeon Moon. Sept, Full Harvest Moon. Oct, Full Hunters Moon. Nov, Full Beaver Moon. Dec. Full Cold Moon.


wish you would list the names of the full moons for the whole year, as in Harvest Moon, Hunter's Moon, etc.

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