NavList:

   

Reply

> Can anyone give a good reference
> for irradiation?

Alex

Perhaps not "good" by your standards, but a book I think you have referenced
in the past, "The Sextant Handbook" by Bruce Bauer, mentions it directly on
page 109, and indirectly on pages 108 and 113.

My copy of Dutton's also mentions it as an optical illusion (page 247,
article number 2232) that "causes the apparent size of a bright or
light-colored object in juxtaposition with a darker one to appear larger
than it actually is."  Bright starts will also appear to have a measurable
diameter.

The net affect will be the horizon of a dark sea will appear depressed
against a light sky, and the Sun will appear larger.  This *mostly* cancels
out in lower limb Sun observations, but it may work against you in
upper-limb Sun observations.

I also suspect it is irradiation that may cause the horizon under the moon
on a moonlighted sea to appear higher than it is.

Dutton's claims the higher the sextant scope power, and the higher the body,
the less affect irradiation will have .

I recall other mentions (perhaps Bowditch?) but the bottom line seems to be
that irradiation is not accurately predictable.

Bill

   

Reply