JulianDateConverter.java

//-----------------------------------------------------------------------------
// JulianDateConverter.java
//
// (c) 2004 Jonathan Stott
//
// Created on 13-Apr-2004
//
// 0.1 - 13 Apr 2004
//  Initial Version
//-----------------------------------------------------------------------------

package uk.me.jstott.util;

import java.util.Calendar;

/**
 * Convert dates to Julian dates.
 * 
 * For more information on using this class, look at
 * http://www.jstott.me.uk/jsuntimes/
 * 
 * @author Jonathan Stott
 * @version 0.1
 */
public class JulianDateConverter {
  
  /**
   * Convert a date/time to a Julian date  
   * 
   * @param date the date the convert
   * @return the Julian date
   */
  public static double dateToJulian(Calendar date) {
    int year = date.get(Calendar.YEAR);
    int month = date.get(Calendar.MONTH)+1;
    int day = date.get(Calendar.DAY_OF_MONTH);
    int hour = date.get(Calendar.HOUR_OF_DAY);
    int minute = date.get(Calendar.MINUTE);
    int second = date.get(Calendar.SECOND);

    double extra = (100.0 * year) + month - 190002.5;
    return (367.0 * year) -
      (Math.floor(7.0 * (year + Math.floor((month + 9.0) / 12.0)) / 4.0)) + 
      Math.floor((275.0 * month) / 9.0) +  
      day + ((hour + ((minute + (second / 60.0)) / 60.0)) / 24.0) +
      1721013.5 - ((0.5 * extra) / Math.abs(extra)) + 0.5;
  }
}