/*****************************************************************************/
/*                                                                           */
/*                                J D                                        */
/*                                                                           */
/*  Program:      JD                                                         */
/*                                                                           */
/*  Programmer:   David G. Simpson                                           */
/*                NASA Goddard Space Flight Center                           */
/*                Greenbelt, Maryland  20771                                 */
/*                                                                           */
/*  Date:         June 23, 2004                                              */
/*                                                                           */
/*  Language:     C                                                          */
/*                                                                           */
/*  Version:      1.00b  (August 24, 2006)                                   */
/*                                                                           */
/*  Description:  Print current value of Julian day (based on system clock). */
/*                                                                           */
/*****************************************************************************/

#include <stdio.h>
#include <time.h>

double julian (int year, int month, double day);



/*****************************************************************************/
/*  main()                                                                   */
/*****************************************************************************/

int main(void)
{
struct tm *systime;
time_t t;
double jd, day, jd_jan0;
int ut_offset;
char day_name[7][10] = {
   "Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday" };


t = time(NULL);
systime = localtime(&t);

if (systime->tm_isdst)
   ut_offset = 4;
else
   ut_offset = 5;

day = systime->tm_mday + (systime->tm_hour+ut_offset)/24.0 + systime->tm_min/1440.0 + systime->tm_sec/86400.0;
jd = julian (systime->tm_year+1900, systime->tm_mon+1, day);
jd_jan0 = julian (systime->tm_year+1899, 12, 31);

printf("\nDate: %.2d/%.2d/%.4d\n", systime->tm_mon+1, systime->tm_mday, systime->tm_year+1900);
printf("Day:  %s\n", day_name[systime->tm_wday]);
printf("Time: %.2d:%.2d:%.2d  UTC\n", systime->tm_hour+ut_offset,  systime->tm_min,  systime->tm_sec);
printf("DOY:  %3d\n", (int)(jd-jd_jan0));
printf("JD: %15.5f\n", jd);

return 0;
}



/*****************************************************************************/
/*  julian()                                                                 */
/*****************************************************************************/

double julian (int year, int month, double day)
{
long a, b;
double jd;


if (month <= 2)
   {
   year--;
   month += 12;
   }

a = year/100;
b = 2 - a + a/4;

jd = (long)(365.25*(year+4716)) + (long)(30.6001*(month+1))
     + day + b - 1524.5;

return jd;
}