Lines in the Sky: what was that strange scene at sunset Monday?

Several photos of the lines across North Alabama’s sky came into WHNT News 19 on Monday evening asking “what in the world is this?!?”

It’s simple: a cloud shadow.

Visible satellite imager and the view from Monte Sano Monday afternoon showing the cumulus field causing the shadows in the sky

We’re able to see about 6 miles of sky from horizon to horizon (from ground level), so what Beverly Mishue and Laura Hodge saw in these photos was the shadow cast from a distant, tall cumulus cloud (likely one more than 60-70 miles away from their vantage point):

Don’t believe that?

This is what it looks like from above when that happens as the International Space Station orbited above the North Pacific Ocean (latitude 14.3, longitude -102.4) on 19 May 2011 at 12:20:26 GMT. (7:20:26 AM CDT)

Clouds and their long shadows photographed as the International Space Station orbited above the North Pacific Ocean (latitude 14.3, longitude -102.4) on 19 May 2011 at 12:20:26 GMT:

Clouds and their long shadows photographed as the International Space Station orbited above the North Pacific Ocean (latitude 14.3, longitude -102.4) on 19 May 2011 at 12:20:26 GMT:

Those shadows happen more often than you would think (as do crepuscular and anticrepuscular rays).

It’s the same ‘shadow,’ by the way, you just see the part of the shadow on the sun’s side of the sky more often than the fainter, less contrasted view on the opposite side.

The above photo from the International Space Station is a great example of how light travels in a straight line (physics experts just heard nails on a chalkboard).  Light is both a particle and a wave, and as long as there is nothing blocking it, that wave will travel in a straight line.  Yes, it’s true that light also scatters when it hits something (that’s why we’re actually able to see anything at all), and it can be bent by gravity, refracted in water or a pane of glass, etc.; however, in general it can be understood that light follows a straight line pattern.  That’s why we get straight shadows like those seen here.  (Straight is in the eye of the beholder, by the way.)

Looking for the forecast? It’s always online at WHNT.com/Weather and in the “Daily Forecast” section on Live Alert 19!

-Jason
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