Simulation of a Blank-Strip Sunset


Here's the sunset for the 2-degree inversion between 50 and 60 m, seen from the bottom of the inversion.

The ray curvature in the inversion is nearly twice the curvature of the Earth's surface, so we have a duct. The observer is in the location that offers the widest blank strip: the base of the inversion, 50 m above the sea.

animation of a blank-strip sunset

Main features

Of course, the most prominent feature is the blank strip: a dark band, centered on the astronomical horizon, that blocks our view of the Sun. As the Sun sinks toward the strip, it flattens out, as if the lower limb were repelled by the strip.

Then a red flash appears below the strip. It rapidly expands into a blob that becomes a highly distorted image of the Sun.

In contrast to the mock mirage, the blob never joins the main image above it; the blank strip completely hides the Sun. Notice that the part just beneath the blank strip is inverted; this mirage is Wegener's Nachspiegelung.

The erect image above the blank strip, and the thin mirage below it, rapidly shrink to thin lines at the edges of the strip. These edges soon fade away; the animation isn't able to show this properly, so it makes them appear to shrink in length, as the ends are thinnest and disappear before the middle.

A few more realistic images of this sunset are shown on another page.

© 2005 – 2008 Andrew T. Young

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