I actually just came across some great code that NOAA uses for sunrise/
sunset/other ephemeris calculations here:

http://www.srrb.noaa.gov/highlights/sunrise/calcdetails.html

they give their source as "Astronomical Algorithms" by Jean Meeus.
They have this js routine:

//
***********************************************************************/
//* Name:    calcDayOfYear                                              */
//* Type:    Function                                                   */
//* Purpose: Finds numerical day-of-year from mn, day and lp year
info  */
//* Arguments:                                                          */
//*   month: January = 1                                                */
//*   day  : 1 - 31                                                     */
//*   lpyr : 1 if leap year, 0 if not                                   */
//* Return value:                                                       */
//*   The numerical day of year                                         */
//
***********************************************************************/

function calcDayOfYear(mn, dy, lpyr)
{
  var k = (lpyr ? 1 : 2);
  var doy = Math.floor((275 * mn)/9) - k * Math.floor((mn + 9)/12) +
dy -30;
  return doy;
}

I haven't tested it, but it's what they use for all their online
calculators, so take that for what it's worth.


On Nov 16, 11:46 am, wytten <[email protected]> wrote:
> Using GWT 1.5.3 it is not immediately obvious to how to convert a
> java.util.Date into a Julian date (i.e, compute day of year).  Is
> there some way to do this without rolling your own?  Thanks.

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