Day and night sides of Earth at the instant of the September 2013 full moon (2013 September 19 at 11:13 Universal Time).
Image via Earth and Moon Viewer
” Simply stated, the Harvest Moon is the full moon that falls the closest to autumnal equinox, which in 2013 comes on September 22. So the full moon that comes tonight and early tomorrow – September 18-19, 2013 – is the Harvest Moon. The moon reaches the crest of its full phase at 11:13 Universal Time on September 19 (6:13 a.m. CDT, in other words before sunrise tomorrow for most of us in the U.S.).
In eastern Asia, on the other hand, the moon will turn precisely full after sunset on September 19. In that part of the world, the full Harvest Moon will be said to take place on the night of September 19-20, coinciding with the yearly Mid-Autumn Festival, sometimes called the Moon Festival.
So watch for the bright full moon both tonight and tomorrow night. Even on September 20, the moon will still be displaying some Harvest Moon characteristics, such as rising close to the time of sunset.
Although the full moon happens at the same instant worldwide, it also occurs at all hours around the clock, depending upon one’s time zone. For instance, for the time zones in the continental U.S., the full Harvest Moon will arrive on September 19, at precisely 7:13 a.m. EDT, 6:13 a.m. CDT, 5:13 a.m. MDT or 4:13 a.m. PDT. For all but the eastern part of North America, the moon will turn precisely full before sunrise on September 19, 2013. Although the moon will appear full all night long tonight – from dusk till dawn – astronomers define full moon as that instant when the moon lies most directly opposite the sun for the month. From our vantage point in North America, we can say the Harvest Moon shines on the night of September 18-19.”