About - Submit Optics Picture of the Day Galleries Previous Next Today  


Moonset, Anchorage, Alaska  ~  Doug Short imaged for eight minutes on February 19, ‘16. The moon passes through a distorting layer of stacked - but minor - temperature inversions. Cold air below warmer. Rays crossed between different temperature and density regions. They refracted, shifting lunar features out of place, even breaking the moon into pancake slices. Finally the upper limb shows a strong green rim. Almost, but not quite, a green flash.     All images ©Doug Short, shown with permission
The moon high in the sky on the same morning.

Refraction through an inversion layer - too oversimplified.

Rays passing from lower temperature and therefore denser air to warmer (blue to orange) are always refracted towards the cooler region. Rays leaving a warmer region into cooler air refract away from the warmer one.

In a strong inversion up to three ray paths might be possible generating three image slices.

Here the moon has only started dipping into the inversion layers. The northern section dominated by the Mare Imbrium bordered at top by Sinus Iridum and Plato remain relatively undistorted.

Between the inversion layers there is less distortion. Features like the Bay of Rainbows and the crater Plato survive.