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A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Which diameter of the sun in digital photos ?
From: Marcel Tschudin
Date: 2009 Aug 21, 14:49 +0300
From: Marcel Tschudin
Date: 2009 Aug 21, 14:49 +0300
For investigating the refraction near the horizon I perform systematic observations by photographing sunsets. So far I used the horizontal diameter of the sun as a reference scale (pixel per degree) for measuring the sun's position above the apparent horizon. Recently I compared this scale to one derived from pictures of landscapes and found to my surprise that they differ by around 8%; the sun is systematically slightly larger. The scale in landscape photos has been measured with distinct features and the distances measured with Google Earth. The scale for (not overexposed) sun photos has been calculated with the angular size of the sun for the corresponding days; this size is based on the sun's diameter (of the photosphere) and the earth's distance. The difference is not related to refraction since the measurements are made in horizontal direction. Any idea, why those two scales differ? It is known that some CCDs have a leak in the IR, also the one in my camera. Could this be responsible for it? Does anyone know more on this? Marcel --~--~---------~--~----~------------~-------~--~----~ NavList message boards: www.fer3.com/arc Or post by email to: NavList@fer3.com To , email NavList-@fer3.com -~----------~----~----~----~------~----~------~--~---