Home > Concepts, Ephemeris Program > 08/24/2021 – Ephemeris – The Harvest Moon is coming next full moon

08/24/2021 – Ephemeris – The Harvest Moon is coming next full moon

August 24, 2021

This is Bob Moler with Ephemeris for Tuesday, August 24th. Today the Sun will be up for 13 hours and 36 minutes, setting at 8:33, and it will rise tomorrow at 6:57. The Moon, 2 days past full, will rise at 10:00 this evening.

We are at that time of year when the advance in Moon rising times from night to night is shorter than the average 50 minutes per night. Tonight the Moon will rise only 21 minutes later than it did last night, and tomorrow’s Moon will rise 20 minutes later than it will tonight. It’s what I call the harvest moon effect, though Harvest Moon will be next month. I find the effect lasts for three full moons, centered on the start of autumn. That’s because the angle of the Moon’s and also the Sun’s paths in the sky called the ecliptic intersect the horizon at a shallow angle near sunset. It’s also the reason Venus will stay close to the western horizon for its evening appearance this year. The planets also hang around the ecliptic, where the zodiacal constellations are.

The astronomical event times given are for the Traverse City/Interlochen area of Michigan (EDT, UT – 4 hr). They may be different for your location.


Autumn vs spring sunset ecliptic

The autumn vs spring sunset ecliptic (orange line). I’m using the autumnal equinox 2021 and vernal equinox 2022 as examples. At the autumnal equinox sunset, the ecliptic runs low in the south, and the ecliptic meets the horizon at a low angle. At the vernal equinox in March, the ecliptic runs very high in the south. It meets the horizon at a steep angle. Click on the image to enlarge it. Created using Stellarium and GIMP.

Near the autumnal equinox, the ecliptic appears low in the south at sunset. Planets near the Sun like Venus are seen low in the west and set soon after sunset. At the opposite end of the sky, a rising Moon near full will rise at less than the 50 minutes later each night average.

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