20200929-1003 Harvest Moon Timescape
The Harvest Moon isn't like the other Full Moons. Throughout the year, the Moon usually rises an average of about 50 minutes later each day. But for the few nights around the Harvest Moon, the Moon rises at nearly the same time, only about 13 minutes later each evening. This is because around the time of the autumnal equinox, the Moon's orbit on successive nights is more nearly parallel to the horizon and its relationship to the eastern horizon does not change appreciably from night to night. Moonrises at Harvest Moon time keep the bright, gorgeous lunar orb seemingly pinned to the twilight sky for several nights in a row. This Harvest Moon effect is more noticeable the further north you live.
An exceptional run of warm days with mostly clear skies (no doubt caused by the mythical "full moon clearing effect") as September 2020 gave way to October afforded an opportunity to photograph the Harvest Moon effect. For four consecutive evenings (Sep 29 to Oct 2), I set up at my favorite spot on Valleyview Drive to photograph the moonrise. Another commitment prevented me from doing a fifth evening, so I transferred my gear to fellow skyscape shooter Alister Ling who kindly shot the moonrise for me on Oct 3.
The result is a composite image showing the Harvest Moon on five consecutive evenings (from right to left: Sep 29 to Oct 3) rising above Edmonton's river valley festooned with the colours of autumn and the University of Alberta's western main campus skyline reflecting the evening twilight glow.
From Valleyview Drive, the eastern horizon is obscured by the local skyline so the image shows the Moon at an altitude of 2.5 degrees. The image confirms a personal observation that a day on either side of Full Moon (the middle moon in the image), one can't tell that the Moon isn't fully full without a closer, more determined look. But two days on either side of Full Moon, with even a casual look, one can see that the Moon is not quite round.
An annotated version of the image, showing the horizon line and the location/time of each moonrise, is here:
All images were taken with a Canon EOS 60D at ISO 200, with a Canon EF-S18-55mm lens at f/6.3 and a focal length of 40mm. The foreground is a two-panel panorama stitched with Hugin. The final composite image was layered and blended with GIMP.
1. For a more detailed explanation see:
2. Viewers may notice that Mars was in the vicinity of the Harvest Moon on Oct 2.
Essential Moonrise Data
Moonrise Moon at Altitude 2.5
Date Time D Az D ILL Time Az
2020 09 29 19:11 106.6 97% 19:33:30 110.9
2020 09 30 19:25 +14m 98.4 -8.2 99% 19:46:30 102.4
2020 10 01 19:38 +13m 90.0 -8.4 100% 19:59:00 93.9 FM 15:05
2020 10 02 19:51 +13m 81.6 -8.4 99% 20:11 50 85.6
2020 10 03 20:04 +13m 73.5 -8.1 96% 20:26:20 77.6