The Sky This Week, 2014 September 2 – 9 — Naval Oceanography Portal

Full Moon occurs on the 8th at 9:38 pm Eastern Daylight Time.  The Full Moon that occurs closest to the Autumnal Equinox is popularly known as the Harvest Moon.  This year the Full Moon of September beats the October Full Moon by one day for this distinction.  In addition to a catchy name, the Harvest Moon also describes a phenomenon that occurs at this time of the year in which the times of successive moonrises around the time of Full Moon differ by about half an hour instead of the more usual one hour.  This effect becomes more noticeable in more northerly latitudes; residents of Stockholm in Sweden see successive moonrises just over 20 minutes later each night.  Folks in Tromsø, Norway will find Luna rising at about the same time for the nights around Full Moon; north of about 70 degrees latitude Luna actually rises earlier for several nights!  This phenomenon once assisted farmers bringing in their crops by providing the light of the rising Moon to assist them in their labors, allowing them to work late into the night.

The last few weeks of astronomical summer produce another subtle change in the night sky.  This is one of two times during the year that the length of daylight changes at its most rapid rate.  In the spring we all notice the days getting longer, and now we see the opposite effect.  Most of us notice this at the time of sunset, which occurs about two minutes earlier each day as we approach the equinox.  Since the stars set four minutes earlier each day throughout the year, the net effect is that the constellations seem to slow their passage across the sky in the fall, so the stars of summer will seem to linger with us well into November.

The Sky This Week, 2014 September 2 – 9 — Naval Oceanography Portal