View Full Version : When Does the Sun Rise… Really?

2019-Jan-31, 11:00 AM
It's strange but true... we may not fully understand one of the simplest metrics in observational astronomy: just what time does the Sun rise... really?
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2019-Jan-31, 12:47 PM
In my opinion "we may not fully understand" is a poor choice of words. As an exercise in physics we understand perfectly well the fact that local variations in atmospheric conditions can throw the refraction calculations off. We also know that the data needed for corrections is not always available in a given situation. As for navigation, it could be worse. Cloudy weather will conceal the Sun entirely, not to mention the stars that would have been used for a fix an hour or so earlier. Navigators will deal with it the way they always have, which is careful dead reckoning since the last good fix. If the time of the first speck of the Sun is seriously amiss, a few minutes will elevate the Sun enough to reduce if not eliminate the problem. A navigator who relies solely on that first speck deserves to be keelhauled. Fortunately the U.S. Navy did away with keelhauling a long time ago.