As I do on occasion, sometimes my post is just to share a “pretty picture.” Search my blog for that term and you’ll see a few more. This week it’s a striking “split sunset” I saw just a few weeks ago after our last rains. You can see the deep red glow of the now-set Sun at lower-right. The usual sunset panorama of orange sky seems to be split, as if caught in a slideshow “wipe” transition to blue sky.
Of course, what we’re seeing is simply the shadow of a cloud between us and the Sun. Trace that shadow line from left to right and you’ll find it points directly toward the Sun’s residual glow. You see that same geometry with crepuscular rays. The cloud casting that shadow may or may not be visible, given how low the Sun is — it could be well below the horizon of those distant mountains and still cast its shadow overhead.
Note how the blue sky on the right looks about like it would during “normal” twilight. The left side of the sky is colored with the red and orange light produced by Rayleigh scattering, but when a large enough cloud blocks that light the sky is left with its usual pale blue color. Where that blue light comes from is explained in my July 27, 2015 post.
Next Week in Sky Lights ⇒ If All Earth’s Ice Melted