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Harvest & Hunters Moon
Most professional astronomers, when asked to name the twelve moons of Earth, might be inclined to gently correct the questioner. Our planet has just one Moon, not a dozen!
But ask any farmer and they'll explain that there are indeed twelve, including the Strawberry Moon, the Buck Moon, the Pink Moon, and every now and then a Blue Moon! They're really all the same moon, but long before the advent of modern calendars people named the Full Moons of a year to keep track of time. These fanciful names have been handed down through the generations and they are still a part of modern Moon lore.
The Harvest Moon is no ordinary full moon -- it behaves in a special way. Throughout the year the Moon generally rises about 50 minutes later each day. But near the autumnal equinox the day-to-day difference in the local time of moonrise is only 30 minutes.
That comes in handy for northern farmers who are working long days to harvest their crops before autumn. The extra dose of lighting afforded by the full moon closest to the equinox is what gives the Harvest Moon its name. In the southern hemisphere, this Full Moon behaves in exactly the opposite way. South of the equator, there will be an extra long time between moonrises from one evening to the next.
Like all full moons, this year's Harvest Moon will be bright and beautiful. Still, there could be an extra treat for Moon-watchers who venture outdoors near dusk or dawn. Wildfires in North America and dust storms in Africa have filled parts of our atmosphere with aerosols. A low-hanging Moon seen through such dusty air can take on a beautiful pink or orange hue. The rising or setting Moon also looks much bigger than it does when it's high in the sky -- a trick of the eye known as the "Moon Illusion."
Farmers on Earth are more fortunate that our planet's moon moves at a relatively leisurely pace, completing one orbit in 29.5 days. Harvest Moons on Earth cast their bright light all night long, and careful timing is not required to see one.
During the months of September and October in the northern hemisphere, the rising of the Moon on successive days following full moon gives rise to what used to be called Harvest and Hunter's Moons. I say "used to" because the relevance of the Moon in the night sky as an aid to work outside after sunset has lost much of its significance. In an age where tractors and other machinery are equipped with powerful headlamps and so forth (to say nothing of floodlit golf courses, football and cricket pitches) the light provided by even a full moon can seem meager if not irrelevant.
Despite this the old terms should be understood. For example, many people appear to be under the impression that the Harvest Moon only applies to the full moon itself at or around the autumnal equinox. The real significance of the term has more to do with the rising of the Moon at or very nearly the same hour on successive evenings and nights from about the time of full moon. This event is particularly noticeable from high northern latitudes.
Consider the motion of the Moon about the Earth which makes it appear to move from west to east against the star background at the rate of approximately 13 arc degrees in a 24 hour period. (Do not confuse this movement with the diurnal motion which the Moon partakes in common with the planets, Sun, stars etc.) Were the Moon to follow a path close to the celestial equator (or parallel to it), then the Moon's rising would be retarded by a little under one hour every 24 hours. However, in common with most of the planets and the Sun, the Moon keeps fairly close to the path of the ecliptic (the plane of the Earth's orbit projected onto the celestial sphere).
From the northern hemisphere in autumn the ecliptic makes a shallow angle with the eastern horizon. As a result, the Moon's increasing declination following full moon offsets its easterly motion in Right Ascension causing it to rise progressively north of east for about a week.
Thus, although the Moon's phase decreases from night to night following full moon (and therefore its contribution to lighting the night sky also diminishes), its presence does add some light to the sky before midnight on a number of consecutive nights at the season associated with harvest (and in some localities, hunting