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

Yes, refraction can be a big factor.

Ya'll might enjoy this view of a flattened Sun:
http://www.phys.ufl.edu/~avery/course/3400/atmosphere/sun_pillar2_minnaert.j
pg

This "floating" iceberg mirage is a dandy:
http://www.phys.ufl.edu/~avery/course/3400/atmosphere/mirage_iceberg.jpg

Other interesting evidence that supports a round Earth include the shadow of
the Earth as seen from a mountain. This is noted by the colorful Belt of
Venus: http://apod.nasa.gov/apod/ap060723.html

The Earth's shadow reveals curvature as it rises when the Sun sets. This
is easier to see when in the mountains looking westward across a plain or
valley. It is also noticeable, however, when the entire region is flat. [I
see it regularly in S. Texas.]

It is my understanding that this observation of curvature was not used for
evidence until a few centuries ago. Then there is the Coriolis effect that
came much later than needed to help with the Earth's shape, but did help
with its motion (rotation).

I have also seen clouds over the Gulf that seemed to be lower than they
should be (for a flat Earth), as well as, project an arched line if their
flat bottoms went across the horizon. It isn't all that obvious,
admittedly, but it stands out if you look for it.

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

Coope

From: asa-owner@lists.calvin.edu [mailto:asa-owner@lists.calvin.edu] On
Behalf Of Randy Isaac
Sent: Thursday, August 21, 2008 1:03 PM
To: asa@calvin.edu
Subject: Re: [asa] Rudwick does it again (back to Adam)

Dave Siemens wrote:

I haven't tried to check the math, but I have stood on the sea shore on a
clear day and seen just the tops of the masts of a vessel, or seen a vessel
sail over the horizon. To what extent does the refraction of the atmosphere
affect this?

Dave (ASA)

A lot! Since we moved to the North Shore Boston three years ago, I've been
fascinated by the visual appearance of ships, lighthouses, the South Shore
of Boston, the Boston Harbor Islands, etc. as observed looking across
Massachusetts Bay. One of my reference points has become a feature known on
the nautical maps as "Halfway Rock." Depending on meteorological conditions,
it sometimes appears to rest precisely on the horizon, sometimes floating
well above the horizon, other times the water and the horizon are easily
visible behind and above the island, still other times the edges are
floating and seemingly curled up, and every position in between. Similar
effects are seen for all the other objects.

I suppose it's been only about a century or so that this effect has been
understand to be refraction of electromagnetic waves through the temperature
differential of the air near the surface, just like the desert mirages. With
more experimental observation, I suspect I could learn to calibrate the
temperature differential between the air and the water based on this effect.

The net is that this effect is so strong and variable, it really dominates.
With no other knowledge or background, I'm not sure that an argument for the
sphericity of the earth would be very obvious or compelling, considering
solely the height of a distant ship.

Randy

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Received on Thu Aug 21 17:12:49 2008