The Traffic Accident Reconstruction Origin -ARnews-

Re: sun position and sunrise/sunset calculations

Ralph Bouwmeester (rba@bconnex.net)
Wed, 16 Apr 1997 13:43:41 -0400 (EDT)

The U.S. Naval Observatory site pointed to by Jim Mitchell in his posting of Apr 14 is a great resource for AR Specialists. Not only can you obtain sun rise and set times based on a specific date and latitude and longitude, you can also get a year's worth of these times based on city name (U.S. cities only though). You can also get daily data based on U.S. city name.

AR Specialists often need "point in time" sun position data, but unfortunately, the USNO site doesn't provide this.

Care should be taken when using the USNO's data if you are inputting your own latitude and longitude since the sun rise and set times generated can be out by an hour. (I guess that the calculations assume certain time zones based solely on longitude, but time zone limits don't always follow straight meridians in 15 degree intervals. Careful !!)

One final caution. In my sun position modelling work, I have come across errors in the assumed latitudes and longitudes used in the USNO database of U.S. city names. It goes without saying that this could really mess things up.

If you need sun position data for one specific date, time and place, contact me directly and I will provide this information for free to any AR Specialist. We also issue free sunrise and set tables for any location upon request.

Ralph Bouwmeester
rba@bconnex.net

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