Spooky season is almost upon us — and this year it will be a little bit spookier.
The night sky on Halloween will be illuminated by a blue moon, the second full moon in a month. The relatively rare occurrence happens once every two and a half years on average, according to NASA's National Space Science Data Center.
Every month has a full moon, but because the lunar cycle and the calendar year aren't perfectly synched, about every three years we wind up with two in the same calendar month.
October's first full moon, also known as the harvest moon, will appear on the first day of the month. The second full moon, or blue moon, will be visible on October 31. It's the first instance of a blue moon in the Americas since March 2018.
It's also the first time a Halloween full moon has appeared for all time zones since 1944, according to Farmers' Almanac. The last time a Halloween full moon appeared was for the Central and Pacific time zones in 2001.
The "once in a blue moon" phenomenon does not necessarily mean the moon will look blue on Halloween. While the dark blue tone of an evening sky can affect the coloring we see, Earth's satellite will most likely not appear blue at all.
Typically, when a moon does take on a bluish hue, it is because of smoke or dust particles in the atmosphere, such as during a major volcanic eruption.
When the phrase "once in a blue moon" was coined, it meant something so rare you'd be lucky (or unlucky) to see in your lifetime, according to NASA.
So if anything unusual happens to you on Halloween, there might just be a good reason why.
What is the Harvest Moon? A guide to full moon nicknames
January: Wolf Moon
The names for full moons, especially the most common ones adopted by the Old Farmer's Almanac, generally come from a combination of Native American and Colonial American terminology that have been passed down through generations.
According to the Old Farmer's Almanac, January's full moon was named the Wolf Moon because wolves tend to howl more during this time period.
Other names: Moon After Yule, Old Moon, Ice Moon, and Snow Moon.
February: Snow Moon
February is generally the snowiest month of the year in North America, so its full moon was appropriately nicknamed the Snow Moon, according to the Old Farmer's Almanac.
Other names: Hunger Moon, Storm Moon and Chaste Moon.
March: Worm Moon
March marks the end of winter, which is the first time earthworms start coming out of the ground. The Worm Moon in March is usually the last full moon before the spring equinox.
Other names: Crow Moon, Crust Moon, Sap Moon, Sugar Moon, and Chaste Moon.
According to TimeandDate.com, the Old English or Anglo-Saxon name is the Lenten Moon.
April: Pink Moon
April's Pink Moon doesn't actually appear pink in the sky. It's named instead after the pink flowers – Wild Ground Phlox or Moss Phlox– that start showing up in early spring, according to TimeandDate.com.
April's full moon is also called the Paschal Full Moon in the Christian calendar. The Paschal Full Moon is the first full moon after the Vernal Equinox and is used to determine the date for Easter.
Other names: Sprouting Grass Moon, Fish Moon, Hare Moon, and Egg Moon
May: Flower Moon
May's full moon is simply named the Flower Moon due to the flowers that bloom during the month.
Other names: Corn Planting Moon and Milk Moon.
June: Strawberry Moon
July: Buck Moon
Antlers generally start showing up on male deer during July, giving the month's full moon the name Buck Moon.
Other names: Thunder Moon, Wort Moon, and Hay Moon.
August: Sturgeon Moon
Many Native American tribes would fish for sturgeon during August, thus giving the month's full moon the name Sturgeon Moon.
The fish were once found in much of the U.S. and Canada, but the population has been significantly depleted due to overfishing.
Other names: Grain Moon, Green Corn Moon, Fruit Moon, and Barley Moon.
September: Harvest Moon/Corn Moon
The September full moon is usually the Harvest Moon, which is the full moon closest to the autumnal equinox. However, that sometimes happens in early October instead.
The name Corn Moon is used nearly as often.
Other names: Barley Moon.
October: Hunter's Moon
As previously mentioned, October's full moon is sometimes referred to as the Harvest Moon if it's the closest full moon to the autumnal equinox. However, it's more commonly referred to as the Hunter's Moon. This is because October was when people in the Northern Hemisphere would begin preparing for winter by hunting, slaughtering and preserving meat.
Other names: Blood Moon, Sanguine Moon, Travel Moon and Dying Grass Moon.
November: Beaver Moon
Colonists and Native Americans used beaver furs to keep warm during winter. They'd set traps in November before swamps froze over to make sure they had enough fur for the cold months ahead. Beavers also became more active during November, making it that much easier to trap them, thus the name Beaver Moon.
Due to hunting, the beaver population in North America has dwindled to about 12 million, where it used to be about 60 million, according to TimeandDate.com.
Other names: Frost Moon, Trading Moon, Snow Moon and Mourning Moon.
December: Cold Moon
The naming of December's full moon is pretty straightforward — it's cold in December in most parts of the Northern Hemisphere. More specifically, it's usually the first month in many areas where it gets really cold and stays that way.
Other names: Long Nights Moon, Moon Before Yule, Oak Moon and Wolf Moon.
The Blue Moon has nothing to do with color. Most commonly, a Blue Moon occurs when there are two full moons in the same month. The first would get the traditional name, while the second moon is called the Blue Moon.
An alternative definition considers a Blue Moon the third full moon in an astronomical season with four full moons, according to TimeandDate.com. A typical season has three full moons.