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Julian Day Numbers
- Subject: Julian Day Numbers
- From: Ben Tupper <pemaquidriver(at)tidewater.net>
- Date: Tue, 14 Nov 2000 09:02:03 -0500
- Newsgroups: comp.lang.idl-pvwave
- Organization: http://extra.newsguy.com
- Xref: news.doit.wisc.edu comp.lang.idl-pvwave:22168
You may have heard the proverb, 'A person with two watches
doesn't know what time it is.' It seems to be true for me.
I have been tinkering with making tidal predictions which,
of course, are dependent upon time. A number of benchmark
are used to establish the phase difference for each harmonic
component calculated. One of the benchmark dates is Noon,
Jan 1, 1900.
IDL> Print, JulDay(1,1,1900,12,0,0)
However, this is just in from a reliable source...
* From the "Explanatory Supplement to the Astronomical
Ephemeris" 1992, p.699
* 1900 JAN 0.5 = JD 2415020.0.
Note the one (1) Julian Day difference. Ugh!
There are a couple of things I could do I guess:
(1) Assume that RSI is ahead of its time, and just charge
(2) Reduce the Julian Day number by one (I hate to do that
since I don't know why I need to.)
(3) Pass different arguments to JULDAY ...
IDL> Print, JulDay(1,0.5,1900)
This item is really just like (2) since JULDAY converts
the input arguments to long integers before processing.
(4) Use the paper tide table published by the local
(5) Post a timely (sorry) question to the newsgroup
regarding what to make of the 1 day difference.
The IDL JULDAY code cites the following reference, but I
don't have it handy to check into.
; Translated from "Numerical Recipies in C", by William H.
; Brian P. Flannery, Saul A. Teukolsky, and William T.
; Cambridge University Press, 1988 (second printing).
248 Lower Round Pond Road
Bristol, ME 04539
Tel: (207) 563-1048