Fall is a very special time of year for sky-watchers. Iconic constellations like Perseus rise in the early evening, as does the sparkling Pleiades cluster, just as the Summer Triangle gradually sinks in the western sky. However, one of the key sights at this wonderful time of year is the Harvest Moon, which occurs this Friday and Saturday depending on where you are on the planet.
Weve just had a new moon supermoon, with one to come later this month, so it should be no surprise that this full moon in the middle is also something rare and speciala Micro Harvest Moon.
What is a Micro Harvest Moon?
You know what a supermoon is. Its when the full moon appears to be larger in the sky than usual because its relatively close to the Earth. The moon has an elliptical orbit, so once in its 29 day journey around our planet its as close as it gets (perigeea supermoon) and once its the furthest it gets (apogeea micro moon). A micro moon looks smaller than usual, so this weekends Harvest Moon is going to be slightly less bright than average. However, if you think that makes any difference to the experience of watching the Harvest Moon close to a horizon, you would be mistaken. Its still going to be a majestic sight.
How, when and where to see the Harvest Moon?
Officially, the moon reaches 100% illumination at the same global time of 4:33am UTC, which is at 5.33 BST a.m./12:33 a.m. on Saturday and 9.33 p.m. PDT on Friday. However, thats not when to observe the Harvest Moon, which is best done by looking to the east at moonrise on Friday or by looking to the west at moonset early on Saturday morning. Find local times for moonrise and moonset for your location.
Technically, Friday evening is the very best time to see a full moon this month, though Thursday and Saturday would do just as well, and even Wednesday and Sunday because the Harvest Moon rises only around 20 minutes later each night. Mostly the moon rises around 50 minutes later each night.
Why is it called the Harvest Moon?
Its all about timing. Traditionally its called the Harvest Moon because a full moon in September coincides with a time when theres a lot of harvesting of crops going on in the northern hemisphere. Since a full moon occurs when the Earth is roughly between the Sun and the moon, it is 100% illuminated and, whats more, it rises around sunset and sets around sunrise. Since it shines all night long, its useful to farmers working late in the fields. Practically speaking, thats been true all week since theres been a waxing gibbous moon since First Quarter moon last Friday.
However, despite the practical nature of Septembers moon, there is a more precise definition; a Harvest Moon is the full moon that occurs closest to the fall or autumnal equinox.
In China the Harvest Moon kick-starts the Mid-Autumn Festival, also known as the Mooncake Festival, while in Japan they celebrate tsukimi (moon-viewing).
When is fall equinox?
The cooling of the weather in September tempts many people to make false conclusions about the seasons. No, fall does not begin on September 1. Its starts on September 23, the date of the fall equinox. Thats the moment when the Sun crosses the celestial equator moving south. Fall has always started then, and always will. It officially marks the beginning of astronomical fall and autumn in the northern hemisphere, and the beginning of spring in the southern hemisphere.
Wishing you clear skies and wide eyes.