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    The taxonomy of refraction
    From: John Huth
    Date: 2011 Jan 7, 07:35 -0500

     Following Marcel's suggestion, I'm trying to work the the taxonomy of refractive phenomena near the horizon, based on the website he supplied.   I'm attaching a few images in the hope that people can suggest "oh, this is a mirage...."   "this is towering..." etc.   

    The reference object is a lighthouse tower that's 50 feet tall at 8 statute miles.  The height of the camera is 25 feet above the surface of the water.   These were taken at different times of the day during the summer.   The water temperature was 70 degrees F, and the air temp varied between 92 degrees F in the first and about 70 degrees F in the last.   I have to look back in the records to find the ambient pressure.

    The first was in midday.   Since I see a partial inverted image of the lighthouse, I'm tempted to classify this as a mirage.   However, I note that the island that it's sitting on (Monomoy) is continuous and is broken into islets in the image.   

    The second was late in the afternoon.   You'll note that there are no inverted images, but the island is still broken up into islets, with some distortion right at the horizon.

    The third is just at sunset.   You can see that the island now appears continuous.   I'm estimating that the air and water temperature were roughly equal at this moment.

    What I don't entirely understand in the first photo is the appearance of an inverted image.   Nominally I associate this with the "hot road mirage", where the surface of a road is hotter than the air above it, causing the inverted image, yet I'm quite sure that the water temperature was below the air temperature when this was shot.   

    John H. 




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