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» Online Classroom   » Tech Support   » StarPilot   » Rise and set times greater than 24 hrs

   
Author Topic: Rise and set times greater than 24 hrs
vjwilliams


 - posted November 29, 2002 01:58 PM      Profile for vjwilliams           Edit/Delete Post 
Rise and set times greater than 24 hrs

Computed rise or set times can end up negative or greater than 24hr. This happens whenever the rise and set phenomena take place on different days from the perspective of the time zone you selected in the UT offsets option. If one of the answers is greater than 24 hr, it means the event has been calculated for the next day, whereas if one is negative it means that one was calculated for the previous day.

If the output is simply being used for planning, you can correct with a +/- 24h and get a result that will likely be right to within a minute or two. If you want more precise values, then adjust the date by 1 and then when you make the 24hr correction you will end up with the value on the date of interest. Note that StarPilot sunrise and sunset times should be a bit more accurate than those in the Nautical Almanac since we use a temperature and pressure sensitive correction for Refraction whereas the Almanac uses a fixed value and we also use a computed SD instead of the fixed value used in the NA. If you want to compare StarPilot values with official Almanac computations you can use the Sun/Moon data from the Naval Observatory.



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