So here is some information regarding the Harvest Moon from Earthsky.
In traditional skylore, the Harvest Moon is the full moon closest to the autumnal equinox, and depending on the year, the Harvest Moon can come anywhere from two weeks before to two weeks after the autumnal equinox. For us in the Northern Hemisphere, the 2013 autumnal equinox comes on September 22, so the September 19 full moon counts as the Northern Hemisphere’s Harvest Moon. If you live in North America, the moon will turn precisely full before sunrise September 19, but from eastern Asia, the moon will turn precisely full after sunset September 19.
What makes a Harvest Moon special? Harvest Moon is just a name. It’s the name for the full moon nearest the autumnal equinox. In the Northern Hemisphere, the Harvest Moon sometimes falls in September and sometimes falls in October. But the Harvest Moon is more. Nature is particularly cooperative around the time of the autumn equinox to make the full moon rises unique around this time.
Here’s what happens. On average, the moon rises about 50 minutes later each day. But when a full moon happens close to the autumnal equinox, the moon (at mid-temperate latitudes) risesonly about 30 to 35 minutes laterdaily for several days before and after the full Harvest moon. Why? The reason is that the ecliptic – or the moon’s orbital path – makes a narrow angle with the evening horizon around the time of the autumn equinox. The narrow angle of the ecliptic results in a shorter-than-usual rising time between successive moonrises around the full Harvest Moon.
These early evening moon rises are what make every Harvest Moon special. Every full moon rises around sunset. After the full Harvest Moon, you’ll see the moon ascending in the east relatively soon after sunset for a few days in a row at northerly latitudes. The lag time between successive moon rises shrinks to a yearly minimum, as described in the paragraph above. Because of this, it seems as if there are several full moons – for a few nights in a row – around the time of the Harvest Moon.
Is the Harvest Moon bigger, or brighter or more colorful? The Harvest Moon is just an ordinary full moon. It isn’t really bigger or brighter or more colorful than any other full moon. But you might think that it is. Why?
It’s true that, in some months, the full moon is closer to us in orbit than others and so truly appears bigger. But the distance of the full moon depends on where the moon is in its orbit. There’s no correlation between each year’s Harvest Moon and the moon’s location in orbit (the actual full moon size). It’s different every year. The 2013 Harvest Moon is pretty close to an average-sized full moon. The biggest full moon for 2013 falls in June. Nowadays, people call these close full moons a supermoon.
Still, you might think the Harvest Moon looks bigger or brighter or more orange. That’s because the Harvest Moon has such a powerful mystique. Many people look for it shortly after sunset around the time of full moon. After sunset around any full moon, the moon will always be near the horizon. It’ll just have risen. It’s the location of the moon near the horizon that causes the Harvest Moon – or any full moon – to look big and orange in color.
The orange color of a moon near the horizon is a true physical effect. It stems from the fact that – when you look toward the horizon – you are looking through a greater thickness of Earth’s atmosphere than when you gaze up and overhead. The atmosphere scatters blue light – that’s why the sky looks blue. The greater thickness of atmosphere in the direction of a horizon scatters blue light most effectively, but it lets red light pass through to your eyes. So a moon near the horizon takes on a yellow or orange or reddish hue.
The bigger-than-usual size of a moon seen near the horizon is something else entirely. It’s a trick that your eyes are playing – an illusion – called the Moon Illusion. You can find lengthy explanations of the Moon Illusion by googling those words yourself.
So be sure to check out the Harvest Moon this coming Thursday. If you get some great photos feel free to share with us on our Facebook page.