Rare blue moon to rise on Halloween night, but don’t expect it to look blue in Chicago
This Halloween, witches on broomsticks can finally fly across a full moon.
For the first time in nearly two decades, a full moon will be spotted in the Chicago sky on All Hallows' Eve, according to experts. It will also be a blue moon, an occurrence that happens when there are two full moons in one calendar month.
A full moon on Halloween is more rare than a blue moon, said Michelle Nichols, director of public observing at the Adler Planetarium. The last time we saw a full moon on Halloween was in 2001.
“You think Halloween and you think it’s a full moon, but it’s hardly ever the case,” she said. “You have to go almost 20 years between seeing a full moon on the actual date of Halloween.”
Given that it takes the moon on average 29 1/4 u00bd days to go around the earth once, we typically see a full moon every month. But, about every 2 1/4 u00bd years, we get an extra full moon in a season, Nichols said.
Blue moons, a term coined by astronomers in the 1800s, are simply a quirk of the calendar system, Nichols said. Longer months sometimes allow the moon phases to repeat.
Contrary to popular belief, full moons do not have an impact on more crazy or unnatural occurrences, though they do add to the holiday’s spooky appeal. Songs, television shows and other pop culture references often misrepresent the uniqueness of the blue moon, she added.
“We don’t always refer to it thinking astronomically and use the term ‘blue moon’ to mean something that doesn’t happen very often, but really it’s something that does happen once every 2 1/4 u00bd years or so,” she said. “It seems more rare than it really is.”
A blue moon can be defined as the second of two full moons in the same month or the third full moon of a season that has four full moons.
The next monthly blue moon after Halloween will occur on Aug. 30, 2023, while the next seasonal blue moon will occur on Aug. 22, 2021, according to the planetarium.
The first full moon in October was a harvest moon, an ode to the history of farmers who depended on the full moon to harvest crops.
“These moon phases favor hunters and farmers because the moon is moving from south to north across the celestial equator, meaning it will be higher and higher in the sky and come up earlier than usual,” said Dan Joyce, a board member of the Chicago Astronomical Society who has studied astronomy for more than 65 years.
Extra light gives farmers more time to harvest crops and hunters more ability to spot prey at night.
Another common misconception is the appearance of a blue tint on the moon during this phase, Nichols said. The moon can appear blue in any phase, and this is caused when there is a lot of dust from smoke particles in the air.
“If you see full moon pictures that are blue, those have probably been photoshopped,” she said. “There’s a next to zero chance for the moon to be blue in Chicago. You can see it in places close to sources of dust, ash and smoke, but in our area, it’s close to zero."
jvillagomez@chicagotribune.com
Twitter @JessicaVillag
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