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The Sky This Week
U.S. Naval Observatory's Weekly Blog
A Howlin' Halloween Hunter's (Blue?) Moon
by Geoff Chester, USNO Public Affairs
27 October 2020
The second Full Moon for the month of October brightens the sky on Halloween, illuminating the night for the trick-or-treaters prowling the neighborhood. Full Moon occurs on the 31st at 6:49 pm Eastern Daylight Time. In popular skylore this Full Moon is almost universally known as the Hunter’s Moon. The same circumstances that cause the Harvest Moon around the time of the autumnal equinox are nearly repeated in October, so the times of successive moonrises in northern temperate latitudes are much shorter compared to other times of the year. As the Harvest Moon aided farmers in reaping their fields, the Hunter’s Moon was thought to aid hunters as they pursued game across the now-barren stubble.
Since the Hunter’s Moon is the second Full Moon in one month this year, many people also call it a “Blue Moon” thanks to a mis-interpretation of a “rule” published in early editions of the “Farmer’s Almanac”. In most years there are three Full Moons occurring in a given astronomical season, and the Almanac bestowed a name on each one. However, about every 2.3 years a fourth Full Moon occurs in a season, upsetting the proper order of the traditional names. To correct this, the Almanac’s writers dubbed the third of these four Full Moons as the Blue Moon, effectively “resetting” the monthly names to match the seasons again. In 1946 a writer for a popular astronomy magazine wrote an article on these “extra” moons, but they didn’t quite grasp the definition, assigning the term to the second Full Moon in a calendar month. Under the Farmer’s Almanac rules, our next “true” Blue Moon will fall on August 22, 2021.
Our modern observance of Halloween is marked by imagery of ghosts, zombies, skeletons, and all things associated with death. I am sure that most of the youngsters clamoring for treats have no clue that they are unwittingly observing an ancient astronomical occasion known as a “cross-quarter” day. Just as there are four seasons in the astronomical year, there are four cross-quarter days as well. These days marked the mid-points between the equinoxes and solstices, and before the Romans spread their calendar across most of Europe these eight annual dates were important ones to celebrate. In particular, the Celts celebrated the cross-quarter days with feasts and bonfires, and their feast of Samhain is the origin of our current Halloween. As the Celts adopted Christianity, they melded Samhain with the Christian All Saint’s Day which occurred on November 1st in the Roman calendar. The night before was reserved to venerate the spirits of the dead, leading to the tradition of welcoming spirits, ghosts, and goblins to the house to be feted with food and drink. Halloween is no doubt the most popular of the cross-quarter days that are still observed in popular culture. Two others, Groundhog Day and May Day, still endure but the fourth one, Lammas (August 1) seems to have fallen out of favor.
Remember to set your clocks back one hour when you go to bed on Halloween. Daylight Time in the U.S. reverts to Standard Time at 2:00 am on November 1st. This annual ritual has never been popular since it was first legislated by Congress in 1918, and today there are a growing number of communities who would like to see it disappear. The history of Daylight Time is complicated, and our current rules are the result of a law passed by Congress in 2005. Fortunately, we at the Naval Observatory are above the fray; we keep Coordinated Universal Time, a single time scale that remains unchanged throughout the year. The laws regarding Daylight Time are the purview of the Department of Transportation. Kindly send your views on the subject to them!
Jupiter and Saturn linger in the early evening sky, dominating the southwest view after twilight fades. They are still well-placed for casual viewing with a telescope, but as their altitude lowers during the course of the night they will only grudgingly give up fine details to the patient observer. Try to catch them early.
Mars is now conspicuous in the east, appearing shortly after sunset as a gleaming red coal in the fading twilight. By the time the sky is fully dark he is very easy to spot, rivalling Jupiter for the brightest planet in the evening sky. Owners of modest-aperture telescopes should look for a prominent feature that’s sometimes called the “eye of Mars”. The Italian astronomer Giovanni Schiaparelli named this feature Solis Lacus (Lake of the Sun), and it is one of the most prominent features on the planet’s disc.
Venus continues to greet early risers in the glow of gathering morning twilight. This week finds our fair neighbor drifting eastward through the stars of the sprawling constellation of Virgo. By the end of the week she will close in on the second-magnitude star Porrima, which she will pass as next week begins.
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