When the immediate environment is characterized with cold temperatures and wispy clouds, a moon around full will often
display the effect commonly referred to as a "lunar halo". Moisture within the wispy clouds will crystallize under
these cold temperatures and, when combined with lunar light, we have refractions within the hexagonal crystals which
lead to the effect depicted by the various phases of the moon below. Furthermore, as is the case with
rainbows, the angle between the incident ray of lunar light
entering the ice crystal(s) and that redirected back to the observer (resultant ray) is known and, in the case of the
lunar halo, measures 22°; thus the size of the lunar halo depicted below is approximately 44° is diameter. Given the
large amount of sky these circles (or halos) cover, they are often missed when looking at the overhead moon.
Note: It is generally believed that a lunar halo is a phenomenon which occurs around full
moon. As indicated by the image below, a nearly first quarter moon provides sufficient light to produce a lunar halo
provided the atmospheric conditions are ideal for such a phenomenon. Furthermore, an extended exposure (15 seconds at
ISO 200) was required and in contrast to a shorter exposure (4 seconds at ISO 100) during
full moon.
Body: Moon Mass: 0.0123 x Earth Mean Eq Diameter: 0.2719 x Earth Distance: 369,538 km Sidereal Rev: 27d 07h 43m 11s Age: 08d 08h 22m Phase: 60.3° Diameter: 32.87' Magnitude: -10.6 Rukl: N/A |
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Date: January 16, 2008 19:09:00 - 19:09:15 UT+2 Location: Athens, Greece Equipment: Canon EOS 300d Canon EOS EF-S 18-55 mm  @ 18 mm / f4.0 Exposure(s): 1 x 15.0 sec ISO 200 JPG FINE Image Format 3072x2048 Image Size Manual Mode Software: Canon ZoomBrowser V5.1 Photoshop CS2 Processing: Levels and Curves Resampling JPG Compression |