Julian date

[Gamma-Ray Burst]

Does anyone know of a pc-compatible program that will either
1) print a calendar for, say 1991, with the julian dates and/or
2) simply provide the julian date as output when a `normal' date is
input?

thanks
jpl

--
John Patrick Lestrade, PhD
Department of Physics and Astronomy
Mississippi State University, MS 39762
Voice: (601) 325-2806 Fax: (601) 325-8898

[Eric Bergman-Terrell]

See the "Date Management" article in the Dec. 1990 issue of Computer Language.
If you're interested in dates B.C., see the "Letters to the Editor" section
of the same magazine, April 1991.

Terrell

[Tom Van Flandern]

John,

> Does anyone know of a pc-compatible program that will either 1) print a
> calendar for, say 1991, with the julian dates and/or 2) simply provide
> the julian date as output when a `normal' date is input?

The following works for the Gregorian calendar from 1901 to 2099:

JDN = 367*Y - 7*(Y+(M+9)/12)/4 + 275*M/9 + D + 1721014

where Y = year, M = month, and D = day, and all math must be done in
integer arithmetic. For example, 8/3 = 2, and the fraction is thrown away.
[If your programming language won't handle 7-digit integers, then let Y =
years since 1900, and change the constant in the above formula to 18314, to
get the so-called "modified Julian day number".]

As an example, for Y = 2000, M = 1, D = 1, then the values of the five
terms are 734000 - 3500 + 30 + 1 + 1721014 = JDN 2451545. [In the modified
formula, Y = 100, and MJD = 51545.]

If there is interest in a formula which works for any Gregorian-
calendar date, the following version also takes account of the century
years which are not leap years, such as 1900 and 2100:

J=367*Y-7*(Y+(M+9)/12)/4-3*((Y+(M-9)/7)/100+1)/4+275*M/9+D+1721029

The value of the new term for the above example date is -15; hence it
yields the same answer as the shorter formula for current dates.

If anyone reading this has related needs, such as the reverse formula
(JDN -> calendar date), or the equivalent formula for the Julian Calendar
(the predecesor of the Gregorian Calendar), send me E-mail. -|Tom|-
--
Tom Van Flandern / Washington, DC / met...@well.sf.ca.us
Meta Research was founded to foster research into ideas not otherwise
supported because they conflict with mainstream theories in Astronomy.