Home > Concepts, Ephemeris Program, Observing, The Moon > 04/27/2021 – Ephemeris – What is the opposite of the Harvest Moon effect?

04/27/2021 – Ephemeris – What is the opposite of the Harvest Moon effect?

April 27, 2021

This is Bob Moler with Ephemeris for Tuesday, April 27th. Today the Sun will be up for 14 hours and 4 minutes, setting at 8:43, and it will rise tomorrow at 6:36. The Moon, 1 day past full, will rise at 9:43 this evening.

Let’s think back to last fall and the Harvest Moon. The big deal about the Harvest Moon is the Moon lingers, rising or being bright in twilight to help illuminate the harvesters of old by effective lengthening the effects of daylight. The spring bright Moon after full moon rises much later night to night. Six months ago the difference in the rise times of the Moon between the full moon and the next day was 20 minutes. Today the Moon will rise 96 minutes later than it did yesterday. The reason is the beside moving eastward, it is also moving southward to where the Sun was in late fall. So it rises much later each night than it did after full moon last fall. As it is the dark skies are moving to later and later in the evening due to the spring season and daylight time.

The astronomical event times given are for the Traverse City/Interlochen area of Michigan. They may be different for your location.


The motion of the moon
The motion of the moon near the Harvest Moon as it rises from night to night. This is looking east at where the Moon will rise, and we’re able to see below the horizon. The celestial equator, a projection of the Earth’s equator on the sky cross the horizon at an angle equal to 90 minus one’s latitude. Around my location that’s 45.5 degrees. The Moon will rise parallel to the celestial equator. Its daily orbital motion is at the shallow angle of 5 degrees. So the advance in rise times starts off at 20 minutes later each night, rather than the average 50 minutes.
Spring Moon rising angle
How the Moon’s path near a spring full moon affects its rise time interval. Note the scale is not the same as the top image. Created using Cartes du Ciel (Sky Charts).
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