Above: Moonrise over Saltsjöbaden, Sweden. Image via Indranil Sinha.
Today – September 6, 2017 – presents the third and final full moon of northern summer (southern winter). In other words, this is the third of three full moons to occur in between the June 21 solstice and the September 22 equinox.
Click here to know the moonrise time, remembering to check the moonrise and moonset box.
Frequently, the September full moon provides the Northern Hemisphere with its Harvest Moon, because the September full moon – more often than not – is the closest full moon to the autumn equinox. But, in 2017, the October full moon happens closer to this equinox, so it’s this year’s Harvest Moon. When the September full moon is not the Harvest Moon, we in North America commonly call it the Fruit Moon, Corn Moon or Barley Moon.
The moon turns precisely full on September 6, 2017, at 7:03 UTC. At North American time zones, that translates to 4:03 a.m. ADT, 3:03 a.m. EDT, 2:03 a.m. CDT, 1:03 a.m. MDT, 12:03 a.m. PDT – and on September 5, at 11:03 p.m. ADKT and 9:03 p.m. HST. By the time that some of you are reading this post, this full moon instant will have passed.
Astronomically speaking, the full moon occurs at a well-defined instant: when the moon is exactly 180o from the sun in ecliptic longitude (also called celestial longitude). That means the moon stands opposite the sun as measured along the ecliptic – the sun’s annual pathway through constellations of the zodiac. Another way of putting it: at the instant of full moon, the moon-sun elongation equals 180o. Click here to find out the present moon-sun elongation (if the number is negative, that means the moon is waning).
To the eye, though, the moon appears full for up to two or three days. So, no matter where you reside on the great globe of Earth, look for tonight’s moon to appear plenty full and colorful as it rises over the eastern horizon at dusk or very early evening.
Thereafter, the brilliant moon will beam all night long!
Bottom line: Full moon is September 6 at 7:03 UTC. So the crest of the moon’s full phase may have already passed, for you. Still, since the moon looks full for several days, we all can enjoy this 3rd and final full moon of northern summer (southern winter) tonight.
Bruce McClure has served as lead writer for EarthSky's popular Tonight pages since 2004. He's a sundial aficionado, whose love for the heavens has taken him to Lake Titicaca in Bolivia and sailing in the North Atlantic, where he earned his celestial navigation certificate through the School of Ocean Sailing and Navigation. He also writes and hosts public astronomy programs and planetarium programs in and around his home in upstate New York.