Distorted Moonset Sequence

February 06, 2012

Lunar Distortion collage EPOD

: Randy Scholten
Summary Author: Randy Scholten; Jim Foster

This photo sequence showing an extraordinary moonset was taken from the shores of Garrison Lake in Port Orford, Oregon. The camera was facing west; looking across the lake, beyond the narrow foredune and out toward the Pacific Ocean. A very clear atmosphere enabled me to watch the Moon set all the way down to the horizon. The distortion that occurred as it descended was quite remarkable -- the Moon's shape was changing as fast as I could snap a picture.

Though we're enthralled with the rising full Moon, we rarely see it set. For one thing, a lot of people are still sound asleep in the early morning hours as the full Moon is working its way toward the horizon. Additionally, our attention is often diverted in the direction of the brightest part of the sky. As the full Moon sets, sunrise, on the opposite horizon, is more captivating than a pale orb that's dimming as quickly as the Sun is rising. However, on this early winter's morn, the Moon did the best it could to make us swivel our heads. The 16-shot moonset sequence begins at 7:10 a.m. (local time) on the morning of January 8, 2012. The Moon was one day shy of being full. I first noticed the Moon's flattened disk (top left) and watched as it changed to a light bulb, an acorn, a square patch of light and finally to a mere slice of itself (bottom right). The "man in the Moon" is hard to see but on the photos at upper right (second and third photos from the right), it appears he's putting on his pants.

Atmospheric refraction is responsible for the distorted shapes. Because the Moon's disk (and the Sun's too) is about half a degree in diameter, light from its bottom passes through slightly more air than at its top as it sets or rises -- the path length of moonlight is greater at the bottom of the disk. Thus, the bottom is refracted upwards more than the top, resulting in the bizarre distortions. Not only was the Moon distorted, but also multiple temperature inversions in effect created multiple Moons -- best seen on second photo from right on top row and in the middle photos of the bottom row. Note also the blue-green glint of light atop the Moon on the bottom row of photos (second photo from left). This is a mock mirage, green flash. What a show!

Photo details: Camera Maker: NIKON CORPORATION; Camera Model: NIKON D700; Lens: 50.0-500.0 mm Sigma APO/DG/HSM f/4.0-6.3; Focal Length: 500mm (35mm equivalent: 500mm); Focus Distance: Infinite;
Aperture: f/6.3; Exposure Time: 2.000 s; ISO equiv: 400; Exposure Bias: -1.67 EV; Metering Mode: Matrix; Exposure: program (Auto); White Balance: Auto; Flash Fired: No; Orientation: Normal; Color Space: sRGB.
All photos were taken within five minutes of each other and none were enhanced in any way -- they're straight out of the camera.