Seeing is Believing

posted Apr 20, 2016, 9:46 AM by Paul Wagner
On a recent post on this blog, we reported seeing both Mt. Shasta and Lassen Peak from the top of the bridge in Terminous, California, about 250 miles away.

Happily, one of our readers pointed out that such a thing was impossible.  Austin wrote to say that Shasta would have to be 40,000 feet tall in order to be visible from 250 miles away.  And he gave us proof: a link to a site that allows you to calculate everything visible from any point you choose:

Which is all really cool, except that we know what we saw.  On a sparkling clear morning with no clouds, we clearly saw the white snowy bumps on the horizon right where Lassen and Shasta should be. 


And, of course, P being an amateur astronomer, he know what must have happened:  atmospheric diffraction.  To quote Wikipedia:  "Terrestrial (atmospheric) refraction usually causes terrestrial objects to appear higher than they really are, although in the afternoon when the air near the ground is heated, the rays can curve upward making objects appear lower than they really are.

Which is exactly what happened that morning in Rio Vista.  We literally saw things that were around the curvature of the Earth.  And if Austin hadn't written to us, we'd never have known.