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No Escape



 From some things there is no escape.

Cary Chieborad gave me a formula for calculating the juliandate and the 
modified julian day?  Jure says it is day, but Cary's document says 
date.  Looks like MJD is what I want as it agrees with the Julian Day that 
people have sent me.  I am now trying to get at the zenith RA so that I can 
calculate where the telescope is pointing.  Jure suggested using the known 
Julian Day for Jan 0.0 2001 which Doug's formula required, and correcting 
with the fractional MJD for the current time.

Starting to do this, it is obvious that Cary's forumla needs UT and not 
local time.  This even though the variables are named things like: 
local->tm_year, local->tm_mday.

OK, so I have set out to convert local time to UT.  Ug!  You don't get off 
easy.  Once you subtract 6 hours (or whatever time zone you are in) This 
requires correction for the number of days in the month through the full 
leap year process.  Let's see, I think it is all years divisible by 4 are 
leap years except those ending in 00?  That should be good 
enough.  Hmmm!  Possibly the right way to do it is to just use Cary's 
formula as if one lived in Greenwich, then subtract the 6 hours from the 
result.

Somewhere there must be a reference page that I can look at that has 
algorithms for all these things?   Can anyone point me to one?  It is 
senseless for me to compute them all from scratch when someone somewhere 
has done it right!

OK, don't think you all are going to get off easy as I struggle with 
this.  I will do the best I can, then put everything I use up for 
criticism.  Then we all will get to live with the result.

Tom Droege