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*Subject*: Re: Julian Day Numbers*From*: Craig Markwardt <craigmnet(at)cow.physics.wisc.edu>*Date*: 14 Nov 2000 15:50:06 -0600*Newsgroups*: comp.lang.idl-pvwave*Organization*: U. Wisc. Madison Physics -- Compact Objects*References*: <3A1145DA.605789C4@tidewater.net> <on8zqm5rqp.fsf@cow.physics.wisc.edu> <3A119BEE.4A5EA1DB@tidewater.net>*Reply-To*: craigmnet(at)cow.physics.wisc.edu*Xref*: news.doit.wisc.edu comp.lang.idl-pvwave:22185

Ben Tupper <pemaquidriver@tidewater.net> writes: > > Thanks, JD, David (I think) and Craig, > > Yes, I agree that the IDL code does calculate what it claims to. My question > was aimed (poorly) at which kind of Julian Day number IDL calculates. > It sounds like it comes in many flavors. I'll punt. No, there is only one flavor here, as long as we are talking about simple Julian Days. If you want January the *0th*, then you'd better enter it as such. Then you get the answer you'd expect: IDL> Print, JulDay(1,0,1900,12,0,0) 2415020.0 The strange thing is that January the 0th is really December 31st. Everybody I know starts counting calendar days with the number 1, so the 0th day of the month is actually the last day of the previous month. So it's strange that your almanac quoted that day instead of January the 1st. There are other conventions, at least in astronomy. The Modified Julian Day (MJD) and Truncated Julian Day (TJD) are very similar time systems, the only difference being the zero-point. Thankfully these systems subtract the 0.5 day that makes standard Julian days so complicated and confusing. [ A day changeover at *noon* ??? ] Craig P.S. Hmm, I had no place for sarcasm here. *(:-) -- -------------------------------------------------------------------------- Craig B. Markwardt, Ph.D. EMAIL: craigmnet@cow.physics.wisc.edu Astrophysics, IDL, Finance, Derivatives | Remove "net" for better response --------------------------------------------------------------------------

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