I did a complete write-up in 2018 on the Hunter’s Moon so, I won’t repeat it, here. That being said, this is a Blue Moon as October’s first full moon fell on…well…the first.
From Moon Giant:
Humans through the ages have always found autumn’s full moons to be creepy and not without good reason. [T]his year, the moon will be extra exciting. The month starts with the Harvest Moon on October 1st and a second Blue Moon on Halloween, October 31st. The Harvest Moon is the Full Moon that falls closest to the Autumnal Equinox on September 22nd. In most years, the September Full Moon lands closest but, this is one of the rare years that the October Full Moon falls very early in the month and closest to the Equinox. This makes the first Full Moon the Harvest Moon and, the second, the Full Hunter’s Moon.
More from Moon Giant:
The modern day definition of a Blue Moon is when there are 2 Full Moons in one month. A Full Moon occurs roughly every 29.5 days and, on the rare occasion when the Full Moon falls at the very beginning of a month, there is a good chance a Blue Moon will occur at the end of the month. Depending on the exact time of the Blue Moon it is possible that some places in the world don’t technically have a Blue Moon. The modern definition […] was derived from an earlier idea of what a Blue Moon was. This earlier definition says a Blue Moon is when there are [four] Full Moons in a season rather than the usual [three]. The Blue moon is the 3rd Full Moon out of the 4. This definition gets a bit complicated and its origins are murky. One school of thought has to do with the naming of the Full Moons. Many cultures named the Full Moons each month to reflect the times for planting, harvesting or seasonal conditions. When an extra Full Moon was thrown in it was referred to as a Blue Moon to keep the Full Moon names constant throughout the year. The idea of a Blue Moon being the extra full Moon in a season (or when there were 13 in a year) was widely used in 19th, and early 20th [century], Farmers Almanacs and the more modern version seems to have come from an article written in the 1930s that misinterpreted the Farmers Almanac definition. The article was titled “Once in a Blue Moon” and from that point on, the term became part of the popular culture.
From Time and Date:
Why is it called a Blue Moon? The historical origins of the term and its two definitions are shrouded in a bit of mystery and, by many accounts, an interpretation error. Some believe that the term “blue moon”, meaning something rare, may have originated from when smoke and ashes after a volcanic eruption turned the Moon blue. Others trace the term’s origin to over 400 years ago. [F]olklorist Philip Hiscock has suggested that invoking the Blue Moon once meant that something was absurd and would never happen. This Halloween Blue Moon […] is also a Micro Full Moon.
100% illumination occurred at 10:49am EDT. ~Vic