
README information for jday and j2d

To unpack the source archive:
	gunzip -c jday-1.2.tar.gz | tar -xvf -

This creates a ./jday-1.2 directory.

To build jday:

	cd jday-1.2
	./configure		(the usual configure arguments are honored)
	make

To install the jday and j2d binaries into /usr/local

	make install

Which creates the binaries /usr/local/bin/jday and /usr/local/bin/j2d

To use:

jday - with no arguments will print out the current Julian date
	based on your system clock and timezone.  If your
	timezone or system clock are inaccurate, the output of
	jday will also be inaccurate

To compute the Julian Date of a particular date/time,
any of the following invocations are allowed::

	jday year
	jday year month
	jday year month day
	jday year month day hour
	jday year month day hour minute
	jday year month day hour minute second

For those items not specified, the current date/time is used.
And for symmetry with j2d output, the format of the output
of j2d can be used:

	jday -d year/month/day hour:minute:second

and in this case all items must be specified.

j2d only operates in one mode.

j2d - must have an argument, which is a julian date.
Output will be in the form: year/month/day hour:minute:second

For example, the following is possible::

	j2d `jday`

To verify correct operation:  (note: there is a year zero in julian dates)

	$ jday -4712 1 1 12 0 0
	0.000000         
	$ j2d 0.0
	-4712/01/01 12:00:00
	$ jday -1 12 31 12 0 0
	1721057.000000   
	$ j2d 1721057.000000
	-1/12/31 12:00:00
	$ j2d 1721058.000000
	0/01/01 12:00:00
	$ jday -d 0/01/01 12:00:00
	1721059.000000  		(why isn't this 1721058 ?)
	$ jday 0 12 31 12 0 0
	1721423.000000   
	$ jday 1 1 1 12 0 0
	1721424.000000   

	$ jday 1970 1 1 0 0 0
	2440587.500000   
	$ j2d 2440587.500000
	1970/01/01 00:00:00

	$ j2d 2451774.726007
	2000/08/18 05:25:27
	$ jday -d 2000/08/18 05:25:27
	2451774.726007

As I was checking these dates, I discovered that there is
something unusual going on at JD 1721058
I don't know what that is, but when I compare all these other
date/time checks with the reference in Jean Meeus, Astronomical Algorithms,
first english edition, 1991, they all check out OK, but he doesn't
mention JD 1721058.  Does anyone know what goes on here ?
There might be a bug lurking somewhere here.  This needs to be
checked out more carefully.

	hiram@cruzio.com - 2000/08/18 05:25:27 - 2451774.726007

