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

Very interesting. Thank you, George. I had been looking for a book on optical effects in the atmosphere so I appreciate the reference.
Thanks for the clarification. I had misunderstood your previous note to imply that the shadow of the earth was somehow connected with the Belt of Venus but now I understand what you said. Is it correct that the pink sky near the sun at sunset is related to Mie scattering but the Belt of Venus is a reflection of such light from Mie scattering?

Randy
  ----- Original Message -----
  From: George Cooper
  To: asa@calvin.edu
  Sent: Friday, August 22, 2008 10:59 AM
  Subject: 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

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Received on Fri Aug 22 11:54:55 2008