Page 68 - Satellite Communications, Fourth Edition

48 Chapter Two

TABLE 2.2 Some Reference Julian Dates
January 0.0 Julian day
1999 2451178.5
2000 2451543.5
2001 2451909.5
2002 2452274.5
2003 2452639.5
2004 2453004.5
2005 2453370.5
2006 2453735.5
2007 2454100.5
2008 2454465.5
2009 2454831.5
2010 2455196.5

For convenience in calculations the day number of the year is given in
Table 2.3.

Example 2.10 Find the Julian day for 13 h UT on 18 December 2000.

Solution The year 2000 is a leap year, and from Table 2.3, December 18 is day
number 335 18 353. This is for midnight December 17/18. UT 13 h as a
fraction of a day is 13/24 0.5416667. From Table 2.2, the Julian date for January
0.0, 2000 is 2451543.5, and therefore the required Julian date is 2451543.5 353
0.5416667 2451897.0417.

In Sec. 2.9.7, certain calculations require a time interval measured
in Julian centuries, where a Julian century consists of 36,525 mean
solar days. The time interval is reckoned from a reference time of
January 0.5, 1900, which corresponds to 2,415,020 Julian days.

TABLE 2.3 Day Number for the Last Day of the Month
Day number for start of day (midnight)
Date Numbers in parentheses are for leap years
January 31 31
February 28 (29) 59 (60)
March 31 90 (91)
April 30 120.5 (121.5)
May 31 151 (152)
June 30 181 (182)
July 31 212 (213)
August 31 243 (244)
September 30 273 (274)
October 31 304 (305)
November 30 334 (335)
December 31 365 (366)