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Watch for September’s full moon

Full moon falls during the night of September 5, 2017 for the Americas, September 6 for much of the rest of the world. It’s not a true Harvest Moon yet, but it acts like one.

Harvest Moon with Century Saguaro (over 100 years old) against the Santa Catalina Mountains of southern Arizona, via Randall Kayfes.

Full moon happens at the same instant worldwide, on September 6, 2017 at 7:03 UTC; translate to your time zone. Here, in the contiguous United States, the moon turns precisely full on September 6 at 3:03 a.m. EDT, 2:03 a.m. CDT, 1:03 a.m. MDT and 12:03 PDT. That’s why we say the full moon falls on the night of September 5, for the Americas.

Is this September full moon the Harvest Moon? Not precisely, but it’ll act like one.

More often than not, the September full moon is the Northern Hemisphere’s Harvest Moon. The Harvest Moon is usually defined as the full moon closest to the autumn equinox, which – in the Northern Hemisphere – comes on or near September 22 each year.

Last year’s Harvest Moon fell in September. Next year’s Harvest Moon will, too.

But, in 2017, the September 6 full moon comes too early to be the Northern Hemisphere’s official Harvest Moon, according to the most widely accepted definition of the term. That’s because the full moon of October 5, 2017, will fall closer to this year’s September 22 equinox. The October 2017 full moon will be this year’s Harvest Moon, while the September 5-6 full moon will carry its ordinary monthly full moon name of Fruit Moon in the Northern Hemisphere (and Worm Moon, Lenten Moon, Crow Moon, Sugar Moon, Chaste Moon or Sap Moon in the Southern Hemisphere). Read more about full moon names.

However, in most respects, the September 2017 and October 2017 full moons can be regarded as Harvest Moon co-stars. By that we mean that both have the characteristics of a Harvest Moon. The primary Harvest Moon characteristic has to do with the moonrise. On the average, the moon rises some 50 minutes later with each passing day. Around the time of the full Harvest Moon, the lag time between successive moonrises is reduced to a yearly low.

In 2017, there’s no appreciable difference between the lag in moonrise times associated with September and October full moons. In both of these months, the moon rises a shorter-than-usual time after sunset for several evenings in a row, following the date of full moon.

Read more about the Harvest Moon

As the sun sets at and near the autumn equinox, the angle of the ecliptic – or sun and moon’s path – makes a narrow angle with the horizon. Image via classicalastronomy.com.

The narrow angle of the ecliptic means the moon rises noticeably farther north (left) on the horizon. For a few to several days after the full Harvest Moon, there is no long period of darkness between sunset and moonrise. Image via classicalastronomy.com.

A full moon is always opposite the sun. That’s why it looks full to us. At full moon, the moon and sun are on a line, with Earth in between. It’s as though Earth is the fulcrum of a seesaw, and the moon and sun are sitting on either end of the seesaw. So as the sun sets in the west, the full moon rises. When the sun is below our feet at midnight, the full moon is highest in the sky. When the sun rises again at dawn, the full moon is setting.

As the moon orbits Earth, it changes phase in an orderly way. Follow these links to understand the various phases of the moon.

Four keys to understanding moon phases

Where’s the moon? Waxing crescent
Where’s the moon? First quarter
Where’s the moon? Waxing gibbous
What’s special about a full moon?
Where’s the moon? Waning gibbous
Where’s the moon? Last quarter
Where’s the moon? Waning crescent
Where’s the moon? New phase

Bottom line: A full moon looks full because it’s opposite Earth from the sun, showing us its fully lighted hemisphere or day side. The September 5-6, 2017 full moon isn’t a true Harvest Moon, but it acts like one.

Can you tell me the full moon names?

Moon in 2017: Phases, cycles, eclipses, supermoons and more

Deborah Byrd