Simulation of an Inferior-Mirage Sunset


The inferior-mirage flash is in fact the one most often seen from near sea level. Here's a simulation of such a sunset.

animation of an inferior-mirage sunset

Even if you stand back to get the naked-eye view, it's clear there's a little green bit at the end of this sunset. But before we take a closer look, notice some special features of this type of sunset, some of which are very well shown in a series of photographs taken by George Kaplan, and displayed on the Naval Observatory's website.

First, there's the “reflection” of the lower limb of the Sun that appears at the horizon. This is actually not a reflection in the ocean, but the miraged image of the part of the Sun a little higher up. During the first half of the sunset, this reflection joins the rest of the solar disk, first forming a shape described by Jules Verne as like an Etruscan vase.

Notice the red upper edge of the reflection, and the red edges of the “neck” it forms as it joins the image above. This is a sort of “red flash”; it's easily photographed in real sunsets.

Then, as the Sun sinks lower, the reflection forms a pair of “feet” at the lower corners of the image. These give the whole image a shape like the capital Greek letter Omega, as was pointed out by the Italian astronomer Annibale Riccò at the end of the 19th Century. This Omega shape is a dead giveaway to an experienced observer of green flashes that there will be a green flash about two minutes later, when the upper edge of the Sun reaches the same height above the horizon as the place where the “feet" of the Omega join the rest of the Sun.

Sure enough, when the top of the Sun sinks to the line where the reflected and erect images join, there's a green flash — and it's visible even on this crude scale. Now, let's take a closer look at it.

© 1999 – 2003, 2005, 2006, 2010, 2014 Andrew T. Young

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