Anticrepuscular Rays and Lunar Eclipse

June 01, 2020

#01 (1)

Photographer: Paolo Bardelli 
Summary Author: Paolo Bardelli

When the sky is clear and the Sun rises or sets behind mountain tops, crepuscular rays may appear if there are a sufficient number of aerosols (dust, pollen, etc.) to scatter light toward the viewer. When crepuscular rays stretch to the opposite side of the horizon, towards the antisolar point, they’re called anticrepuscular rays, as shown in the first photo of the 3 image panel above. This photo was taken in in La Higuera, Chile, at dawn, on July 2, 2019, where on the same day a fantastic total eclipse of the Sun was viewed. 

The orbital plane of our lone satellite is inclined by 5.9 degrees, therefore the Moon-Earth-Sun alignment does not always create the conditions necessary for having an eclipse of the Moon at the time of each full Moon. Simply by looking where the anticrepuscular rays fall in respect to the full Moon, I can tell if a lunar eclipse will occur.

The middle photo was taken on July 27, 2018, from Numana, Italy. The full Moon is rising here exactly at the point of convergence of the solar shadows. Note that this was the longest total lunar eclipse of the century, with a darkening duration of 103 minutes. It was just starting when I snapped the photo.

The bottom photo was taken on October 23, 2018, from Pordoi Pass, in the Dolomites of northern Italy. Here, the Moon rises several degrees to the right of the antisolar point. Thus, there is no opportunity for an eclipse of the Moon to occur, even a partial eclipse.