Bob Ware (14 June 2011)
"correction: Sun halo was only about 5 miles across"

The continental U.S. spans approximately a 50 degree arc of the earth's
surface, but as viewed from the surface of the Earth, an arc of 50
degrees of the clouds (at an altitude of 6 miles) only spans an arc of
about 5 miles in length. So, the halo I saw around the Sun probably
wasn't more than 5 miles across.