Android Long to Date Convert toJulianDayNumber(long epochMillis)

Description

Calculates the astronomical Julian Day Number for an instant.

License

Apache License

Parameter

Parameter	Description
epochMillis	the epoch millis from 1970-01-01Z

Return

the astronomical Julian Day represented by the specified instant

Declaration

public static final long toJulianDayNumber(long epochMillis) 

Method Source Code

//package com.java2s;
/*/*from   w  w  w. ja va2 s .  com*/
 *  Copyright 2001-2012 Stephen Colebourne
 *
 *  Licensed under the Apache License, Version 2.0 (the "License");
 *  you may not use this file except in compliance with the License.
 *  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 *  Unless required by applicable law or agreed to in writing, software
 *  distributed under the License is distributed on an "AS IS" BASIS,
 *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *  See the License for the specific language governing permissions and
 *  limitations under the License.
 */

public class Main {
    /**
     * Calculates the astronomical Julian Day Number for an instant.
     * <p>
     * The {@link #toJulianDay(long)} method calculates the astronomical Julian Day
     * with a fraction based on days starting at midday.
     * This method calculates the variant where days start at midnight.
     * JDN 0 is used for the date equivalent to Monday January 1, 4713 BC (Julian).
     * Thus these days start 12 hours before those of the fractional Julian Day.
     * <p>
     * Note that this method has nothing to do with the day-of-year.
     * 
     * @param epochMillis  the epoch millis from 1970-01-01Z
     * @return the astronomical Julian Day represented by the specified instant
     * @since 2.2
     */
    public static final long toJulianDayNumber(long epochMillis) {
        return (long) Math.floor(toJulianDay(epochMillis) + 0.5d);
    }

    /**
     * Calculates the astronomical Julian Day for an instant.
     * <p>
     * The <a href="http://en.wikipedia.org/wiki/Julian_day">Julian day</a> is a well-known
     * system of time measurement for scientific use by the astronomy community.
     * It expresses the interval of time in days and fractions of a day since
     * January 1, 4713 BC (Julian) Greenwich noon.
     * <p>
     * Each day starts at midday (not midnight) and time is expressed as a fraction.
     * Thus the fraction 0.25 is 18:00. equal to one quarter of the day from midday to midday.
     * <p>
     * Note that this method has nothing to do with the day-of-year.
     * 
     * @param epochMillis  the epoch millis from 1970-01-01Z
     * @return the astronomical Julian Day represented by the specified instant
     * @since 2.2
     */
    public static final double toJulianDay(long epochMillis) {
        // useful links
        // http://en.wikipedia.org/wiki/Julian_day#cite_note-13 - Wikipedia
        // http://aa.usno.navy.mil/data/docs/JulianDate.php" - USNO
        // http://users.zoominternet.net/~matto/Java/Julian%20Date%20Converter.htm - Julian Date Converter by Matt Oltersdorf
        // http://ssd.jpl.nasa.gov/tc.cgi#top - CalTech
        double epochDay = epochMillis / 86400000d;
        return epochDay + 2440587.5d;
    }
}

Related

1. toCalendar(long hour)
2. toDateString(long seconds)
3. toFullDate(long timestamp)
4. toIso8601(long date, boolean utc)
5. toJulianDay(long epochMillis)
6. toString(Long datetime)
7. toTimeString(long milliseconds)
8. stringForTime(long timeMs)
9. getTimeString(long millis)