Archive
09/03/2012 – Ephemeris – Almost the Harvest Moon
Ephemeris for Labor Day, Monday, September 3rd. The sun will rise at 7:07. It’ll be up for 13 hours and 6 minutes, setting at 8:14. The moon, 3 days past full, will rise at 9:21 this evening.
Last Friday’s full moon wasn’t the Harvest Moon. That honor is reserved for the closest full moon to the autumnal equinox, which will occur on the 29th. Still we have the same effect of taking quite a few days for the waning gibbous moon to clear the evening twilight. So tonight the moon, some three days past full still rises within an hour and a half of sunset. In the spring the day after full, the moon will rise an hour and a half after sunset. The reason for the slow advance of rise times is that the moon’s path at this time is at a low angle to the eastern horizon, so the moon moves more horizontally than vertically with respect to the horizon each night. On average the moon moves about 26 times its diameter each day in its orbit of the earth.
Times are for the Traverse City/Interlochen area of Michigan. They may be different for your location.
Addendum
Almost the Harvest Moon Effect over 4 nights. Created using Cartes du Ciel (Sky Charts)
The shallow path of the moon rising from night to night allows the moon to rise much less than the 50 minutes average night to night moonrise interval.
09/12/11 – Ephemeris – Harvest Moon tonight
Monday, September 12th. The sun will rise at 7:17. It’ll be up for 12 hours and 41 minutes, setting at 7:59. The moon, at full today, will rise at 7:43 this evening.
Today’s full moon is the famous Harvest Moon, the nearest full moon to the autumnal equinox. This is a time of the full and waning gibbous moons in the next few days rising in twilight. In the old days before electric lights it helped farmers by effectively lengthening the hours of light to gather in the crops. The moon on average rises 50 minutes later each night. The interval between tonight’s moonrise and tomorrow’s will be 22 minutes. The interval between Tuesday and Wednesday will be 24 minutes, between Wednesday and Thursday, 27 minutes. The instant of full moon today is actually past, at 5:26 this morning. The fact that the rising moon appears orange has nothing to do with the Harvest Moon. Like the sun, it’s always orange or red near the horizon.
* Times are for the Traverse City/Interlochen area of Michigan. They may be different for your location.
08/15/11 – Ephemeris – Preview of next month’s harvest moon
Monday, August 15th. The sun rises at 6:44. It’ll be up for 14 hours and 3 minutes, setting at 8:48. The moon, 2 days past full, will rise at 9:16 this evening.
Last Saturday night under partly cloudy skies at the Port Oneida Fair Star Party we saw the full moon rise and it reminded me that the next full moon will be the Harvest Moon. The next few nights will preview the coming harvest moon effect. That is that the moon will rise at nearly the same time for several nights in a row. On average the moon will rise or set 50 minutes later each night. Due to the geometry of the situation the harvest moon for several nights will only rise later by down to 20 minutes a night. Back before electric lights the bright moonlight augmented twilight to increase the daily time available to harvest the crops. This slowdown in the moon’s rise times is affecting us now, though the moon is definitely waning.
* Times are for the Traverse City/Interlochen area of Michigan. They may be different for your location.
Bob Moler's Ephemeris Blog 