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

Hi Randy,

If you can observe an unobstructed horizon opposite the setting or rising
Sun, you should have little trouble seeing an arch in the dark blue-grey
color band that hugs the horizon. This darker region is the shadow of the
Earth cast upon the horizon before the Sun actually rises or just after it
has set. Because of the miles of shadow you are observing, you will see
Earth's curvature as a result. The higher you are and the broader your
horizon, the easier, it is to see, but it is still fairly easy to see the
curvature in this color band without being on a mountain, as you correctly
stated.

The pink color band in the Belt of Venus is due to "reflected" light of the
reddened Sun. The color of the blue-gray band in the belt is due to our
very thin ozone layer. Ozone has the surprising ability to absorb the
longer wavelength visible colors, so a dim blue color results when sunlight
has traveled through enough of the ozone layer. This ozone color absorption
also explains why you still see a blue sky directly above you when the Sun
is on the horizon. The Rayleigh scattering effect alone would cause the sky
directly above to appear more yellow or red due to the fact sunlight would
have traveled through so much more atmosphere. However, the ozone
absorption prevents this reddening effect, and you still get a blue. It is
said that those who look for the slight blue change in color overhead can
see the difference take place at the appropriate time during sunrise and
sunset, but I haven't tried to do this.

An enjoyable read is "Why the Sky is Blue" - Gotz Hoeppe (2007) , which
addressed many interesting atmospheric phenomenon and with quite lucid
explanations that went into considerable depth (given the simplistic
sounding title). [I had hoped to find his view regarding the Sun's true
color (my pet research project), but he, like most others, ignored or
avoided it.]

"Coope"

From: asa-owner@lists.calvin.edu [mailto:asa-owner@lists.calvin.edu] On
Behalf Of Randy Isaac
Sent: Friday, August 22, 2008 6:35 AM
To: asa@calvin.edu
Subject: Re: [asa] Rudwick does it again (back to Adam)

George Cooper wrote:

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

Many thanks for the info about the Belt of Venus. I have oftened observed it
in the mornings here in Massachusetts but never understood what it was or
what it was called. I'm still not sure I understand it. How does it support
a round earth and what does it have to do with a shadow of the earth? A
mountain doesn't seem to be necessary to see it, either.

Randy

To unsubscribe, send a message to majordomo@calvin.edu with
"unsubscribe asa" (no quotes) as the body of the message.
Received on Fri Aug 22 11:00:19 2008