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Thursday, July 21, 2016

Flat Earth Follies: Crepuscular rays

Many people are confused by Crepuscular Rays because they appear to converge at a point "just behind the clouds" and thus suggest an impossibly nearby Sun. In actuality, they are very nearly parallel to each other and it's just perspective that causes this appearance.

My video below (shot in New Mexico just south of Artesia, 13 May 2016 at 5:45pm, Lat: 32.6847, Long: -104.3956) shows crepuscular rays from a rapidly moving vehicle. Because of this motion you can see that the apparent spray of the rays follows the camera and therefore cannot, at the same time, be the true angle.

You can even see the "depth" of the rays as closer rays move across the field of view more rapidly than further rays and these closer rays completely flip from left-spray to right-spray. The reason for this is that the Sun is very distant, all the rays are actually parallel and are coming in at an angle towards the viewer, and because of this angle only appear to converge due to perspective effects (exactly as train tracks appear to converge in the distance but are clearly parallel).

Our brains are simply not used to evaluating ephemeral rays in 3 dimensions - but hopefully this view helps you to see and understand what the shape of that 3 dimensional volume really is (tilted rays that only appear to converge due to perspective.

Was the Sun directly over me?  No, it was directly over the Pacific, near Latitude: 18° 41' North, Longitude: 176° 55' West. for New Mexico at 5:45pm on 13 May 2016

Here is what is going on from above:

 ISS029-E-31270, October 18, 2011 @ 1132.53Z (rotated)

If we could simply trace the apparent 'sunbeams' to their source then you would have to conclude from the following image that the sun goes down below the surface of the Earth.

APOD 28 November 2010 - Anticrepuscular Rays Over Colorado by John Britton

But these are actually anti-crepuscular rays with the Sun behind the camera -- the apparent converge here is because the rays are parallel overhead and just like the train tracks they appear to converge in the distance.

The following model is from the SketchUp warehouse and I just set up a few views to take some screenshots.  You can DOWNLOAD THIS MODEL (you'll just need Google SketchUp) -- [or the SketchUp 2017 Version Of Model]

It sure LOOKS like our rays converge!

But they don't, as we see in the side and overhead view:

3D Model Side View

3D Model Overhead View

Here is another good example of the converging rays going overhead:

Where is the sun here? The cloud lighting should give it away.

And some examples showing why naively tracing converging lines in a 2D photograph leads to ridiculous conclusions:

Is the sun just outside that window?

Or just behind that tree?

Science Show Video:

Additional Resources:


  1. Also a good thread on Metabunk with more pictures, some showing the Sun would only be about 300 feet away if you could simply "follow the naive angle of the rays".

  2. Last week I was able to snap a photo of some interesting crepuscular rays. I was facing East at close to sunset, so the sun was behind me, but was shining through some storm clouds such that it was creating crepuscular rays pointed away from the sun, but still converging in the distance. I'd love to share the photo with you, but don't know the best way to get it to you.

    1. sir dark star at gmail

      or ping me on twitter @ColdDimSum

      The 'underground' image above is actually what you describe - anti-crepuscular rays :)


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