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    Correcting Night Vision
    From: Frank Reed CT
    Date: 2005 Aug 11, 15:13 EDT
    There's a fascinating article in the latest issue of Sky & Telescope magazine on night vision. It starts out with a detailed account of "night myopia" --that tendency for vision to become unfocused as our eyes adapt fully to darkness. The article suggests that observers (of all ages) who want to see the night sky at its best should consider getting eyeglasses specially made for night use. A prescription 1.0 diopter stronger than normal is suggested as a rough guideline though there are details in the article on doing your own testing. Note that this is not necessary when looking through a telescope (on a sextant or otherwise) since refocusing can correct for night myopia. The article notes that this phenomenon was first described in the scientific literature back in 1789 by none other than Nevil Maskelyne, the Royal Astronomer who can be counted as the grandfather of the Nautical Almanac.
    This same article goes on to discuss the benefits and possible downside of the latest techniques in laser surgery with respect to amateur astronomers and others who value their eyes as precision optical systems. You'll have to read this yourself to get the full story, but there are some nice descriptions of the higher order aberrations in the eye that can lead to distortions in images of stars. This seems relevant to celestial navigators since many people describe star images as appearing "spikey" and "flared" even at the best focus. It's interesting that the latest laser surgery technique captures and corrects for these higher order problems so that star images should come out nearly circular and sharp with effective resolution as good as 20/10 in some cases (20/20 is 1.0 arcminute resolution by definition, 10/10 is 0.5 arcminute resolution --which is right at the theoretical limit for ordinary resolution).
    42.0N 87.7W, or 41.4N 72.1W.
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