Lunar Standstill and Saros Cycle

October 12, 2006

Lunar-scenic-major-standstill-20060903-25pct copy

Provided by: Anthony Ayiomamitis
Summary author: Anthony Ayiomamitis

These unique digital photo mosaics of the Moon and Sun were captured from near Athens, Greece and show the rising Sun and Moon between September 3 and 15. The sequence on the far right was taken on September 3, 2006, whereas the sequence on the far left was taken on September 15, 2006 (just after midnight) -- the middle frame of the rising Sun was also taken Sept 15, 2006.

In regards to the Moon, the period from 2005-2007 is of interest because it represents the end of the current Saros lunar cycle. Mid-September of 2006 was especially noteworthy since it was the time of one of the major lunar "standstills" during this Saros cycle. I exploited this by capturing the rising third-quarter Moon as a time series using exposures spaced five minutes apart. This technique was also employed for the rising Sun, included here as a reference for the ecliptic -- the mean plane of the Earth's orbit around the Sun. The third frame shows the greatest declination of the Moon below the ecliptic but during the same synodic month. Note that the brightness of the afternoon Sun made observations of the nearly first-quarter moon quite challenging. Nonetheless, these three mosaics show the maximum possible deviation in the declination between the Sun and the Moon, which occurs only at the end of each Saros cycle. Lunar eclipses are common during these standstills and this year was no exception (partial lunar eclipse of September 7, 2006).

Although the Moon generally hugs the ecliptic and follows the Sun across the sky, the tilt in the Earth's axis of rotation, relative to the ecliptic (23.45 degrees) coupled with a similar tilt in the Moon's axis of rotation (5.1 degrees), results in a maximum net tilt of 28.55 degrees for the Moon. This leads to dramatic lunar rising and setting declinations in relation to that of the Sun (and the ecliptic).

Note that the electrical wires in the middle portion of the image are missing from the right portion. The local electrical company decided to expand the electrical facilities in this area at the most inopportune time (mid-project for me), and I couldn't convince them to wait a week for my project to come to completion (they had quite a laugh at my request -- and project).

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