Harvest Moon on Friday the 13th

These next several nights – September 12, 13 and 14, 2019 – look for a full-looking moon to light up the nighttime sky from dusk till dawn. Depending on where you live worldwide, this upcoming full moon will fall on Friday, September 13, or Saturday, September 14. For the Northern Hemisphere, this September full moon counts as the closest full moon to the September autumn equinox, so it’s the Northern Hemisphere’s full Harvest Moon.

Read more: Two Friday the 13ths in 2019

In the Southern Hemisphere, the September equinox ushers in their spring equinox. Therefore, the Southern Hemisphere’s autumn equinox will come six months later, on March 20, 2020. And the full moon on March 9, 2020, will be the Southern Hemisphere’s Harvest Moon – the full moon closest to their autumn equinox.

Although the moon appears full to the eye for a few to several days in succession, it is only truly full for a fleeting instant. Astronomically speaking, the moon is full at the moment that it’s exactly 180 degrees opposite the sun in ecliptic longitude. This moment falls on September 14, at 4:33 Universal Time.

The full moon occurs at the same instant worldwide, but the local clock time varies by time zone. At time zones in the mainland United States, the full moon falls on Saturday, September 14, at 12:33 a.m. EDT – yet on Friday, September 13 at all other U.S. times – at 11:33 p.m. CDT, 10:33 p.m. MDT and 9:33 p.m. PDT. The last time that the Northern Hemisphere’s full Harvest Moon fell on a Friday the 13 (for at least a portion of the world) was in the year 1935, and the next time won’t be until the year 2171.

Click here to find out when the moon turns full in your time zone, remembering to check the Moon phases box.

In short, the full moon occurring most closely to the autumnal equinox (the Northern Hemisphere’s September equinox/Southern Hemisphere’s March equinox) enjoys the designation of Harvest Moon. By Universal Time, the full Harvest Moon will come on September 14, 2019, in the Northern Hemisphere – and to the Southern Hemisphere on March 20, 2020.

There is no Harvest Moon at the equator and not enough of one to say so in the tropical regions of the globe. You really have to be well north (or south) of the tropics to observe the year’s grandest parade of moonlit nights around the time of the autumn equinox. The farther north or south of the Earth’s equator you live, the longer the procession of moonlit nights accompanying the Harvest Moon.

In early autumn, at sunset, the angle of the ecliptic – the sun’s yearly path or the moon’s monthly path in front of the constellations of the zodiac – makes a narrow angle with the horizon. Image via classicalastronomy.com.

The term Harvest Moon might be of European origin, because northern Europe is much closer to the Arctic than the tropics. Before the advent of artificial lighting, people planned nocturnal activity around the moon, knowing the moon provides dusk-till-dawn moonlight on the night of the full moon. But farmers of old were also aware that the Harvest Moon – the closest full moon to the autumn equinox – could be relied upon to provide dusk-till-dawn moonlit for several days in a row at mid-temperate latitudes, or even as long as a week straight at far-northern latitudes.

This bonanza of moonlight in the season of waning daylight remains the legacy of the Harvest Moon. The Harvest Moon distinguishes itself from other full moons with several nights of dusk-till-dawn moonlight.

At the vicinity of full moon, the moon stays more or less opposite the sun throughout the night. A full moon (or nearly full moon) rises in the east around sunset, climbs highest up for the night around midnight and sets in the west around sunrise. In this respect, this applies to any full moon at any season of the year.

Yet this closest full moon to the September equinox displays special characteristics for both the Northern and Southern Hemispheres. From around the world, the September full moon rises pretty much eastward. Again, from both the Northern and Southern Hemispheres, you’ll find the moon rising farther and farther north along your eastern horizon each evening for the next week or so. Don’t know which way is north? No problem. As you stand facing eastward, north is your left.

On the average, the moon rises 50 minutes later each day. For us in the Northern Hemisphere, however, the northbound moonrises following the September full moon reduce the lag time between successive moonrises to a yearly minimum. In the Southern Hemisphere, these more northern moonrises increase the lag time between successive moonrises to a yearly maximum.

Check out the chart below.

The narrow angle of the ecliptic means the moon rises noticeably farther north on the horizon, from one night to the next. So, as viewed from northerly latitudes, there’s no long period of darkness between sunset and moonrise. Image via classicalastronomy.com.

From 40 degrees north (Denver, Colorado, or Philadelphia, Pennsylvania), the moon now rises some 25 (instead of 50) minutes later daily. From Anchorage, Alaska (just north of 60 degrees north latitude), the moon rises about 8 minutes later daily.

The higher the latitude, the greater the Harvest Moon effect – the effect of no great lag time between sunset and moonrise – in the season of waning daylight.

By the way, this full moon is also being called a micro-moon or mini-moon because it’s the farthest (and therefore the smallest) full moon of the year. This full moon comes one fortnight (approximately two weeks) after the new moon supermoon on August 30, 2019, and one fortnight before the new moon supermoon of September 28, 2019.

Four years ago, the Harvest Moon of September 28, 2015. presented the closest (and therefore the largest) full moon of 2015.

Super Blood Moon eclipse on September 28, 2015

The September 2019 full moon is the nearest full moon to the September equinox; yet, at the same time, it’s the farthest full moon of the year.

Bruce McClure