Re: [asa] Rudwick does it again (back to Adam)

"Don, I get about 0.87 miles for a 1.5 inches of sinking between them when they are at sea level."

"...A two-meter tall person could see about 3 miles (5060 meters) to the horizon on an earth-sized sphere."
 
 
My apologies. I calculated things in miles and then assumed the answer was in feet! Been retired too long, I guess.
 
An upper limit for the distance a line tangent to the surface of an Earth-like sphere lies above the surface 30 miles away from the tangent point is 600 ft, not 1.5 inches!
 
In consequence I'll need to rethink whether I believe unaided human eyes can reliably detect Earth's curvature by observing how objects "sink" as they move away at sea. Perhaps, under the right circumstances; although there's still the issue of resolving details at fairly large distances. In any case the effect is not obvious to those who aren't looking for it.
 
BTW Crater Lake is in Oregon, not Washington.

Don
 
  ----- Original Message -----
  From: Merv<mailto:mrb22667@kansas.net>
  To: George Cooper<mailto:georgecooper@sbcglobal.net> ; asa@calvin.edu<mailto:asa@calvin.edu>
  Sent: Thursday, August 21, 2008 4:05 PM
  Subject: Re: [asa] Rudwick does it again (back to Adam)

  George Cooper wrote:

    [Don, I get about 0.87 miles for a 1.5 inches of sinking between them when they are at sea level. ]

    Coope

  Maybe my earlier corrections on this weren't seen, but a two-meter tall person could see about 3 miles (5060 meters) to the horizon on an earth-sized sphere. Hence the inability to see an opposite shore line on a lake more than 3 miles across. (disregarding refractive effects.)

  Or the 1.5 in. height George notes above would have a horizon about 0.43 miles away, or you could get the 0.87 mi figure as the distance apart that two 1.5 in. tall figures could see each other over the horizon 'hump' centered between them. But on that scale, even the slightest waves overwhelm any precision. And for longer and larger heights & distances refraction, atmospheric haze and such begin to impose their limitations. But for intermediate distances, such as over a large calm lake this effect is actually quite observable --especially with a good pair of binoculars.

  (When I email from school it comes through under mrb22667@kansas.net<mailto:mrb22667@kansas.net> --I hope those emails have been getting through.)

  --Merv

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Received on Fri Aug 22 03:48:04 2008