Paraselene and Pooch
January 16, 2020
Photographer: Marcella Giulia Pace
Summary Authors: Marcella Giulia Pace; Jim Foster
Shown above is the waning gibbous Moon as observed over the Modica countryside of Sicily, Italy on the night of December 15, 2019. At right center is a parselene or moon dog. Although 22-degree lunar halos are commonly seen when the Moon is in the gibbous and full phases, other halos features, such as moon dogs are rarely noticed since the Moon’s light is too feeble to make them as conspicuous as their daytime counterparts (sundogs). They’re formed when moonlight moves through oriented, hexagonal, plate-shaped ice crystals. These crystals are either free-falling in the atmosphere or more likely, contained in cirrus clouds. As moonlight enters one of the crystals’ side faces it’s bent by approximately 22 degrees before exiting an alternate face. Thus, they’re seen 22 degrees away from the Moon and also at the same altitude as the Moon
Moon dogs can only be seen when the Moon’s not too high up in the sky (below 61 degrees above the horizon or 29 degrees from the zenith). As can be seen at bottom center, these moon dogs aren’t the only dogs visible on this photo. My pooch made an unexpected appearance as I snapped the shutter.
Photo Details: Camera: NIKON D7100; Software: Adobe Photoshop CC 2014 (Macintosh); Exposure Time: 30.000s; Aperture: ƒ/2.8; ISO equivalent: 100; Focal Length (35mm): 16; Lens: Tokina AT-X 116 PRO DX 11-16mm F2.8.