File: dosephem.txt

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   HELP FOR GENERATING EPHEMERIDES IN CONSOLE FIND_ORB

   You can enter the times of the start and end of the ephemeris in
year/month/day, such as "2008 7 31" (or "2008-jul-31").  Or you can specify
'now';  the time will be rounded to the nearest step size. If you want the
ephemeris to start a week ago, use 'now-7'.  For ten hours from now,  use
'now+10h'.  Or you can enter a Julian Day,  such as '2451545.0'.  (Still
more options for time entry are listed below. Note that you can use the same
methods to enter an epoch or to search for observations by date.)

   The step size is a number,  positive or negative,  followed by 'm',
'h',  's',  'd',  or nothing (which defaults to days).  For example,
if you wanted the ephemeris to have a ten minute stepsize,  use '10m'.

   Hit '-' to reverse the sign of the step size.  Hit 'Alt-D' to get a
default start time ("now") and geocentric observable ephemerides.

   If you specify the start time and step size and then hit 'e',  you can
enter an end time.  Find_Orb will adjust the number of steps to match.

   You can have motion details (total apparent motion in '/hr = "/min plus
position angle),  alt/az data,  radial velocity,  and/or phase angle data
in the ephemerides.  These can be toggled with 'z', 'a', 'c', and 'p',
respectively. Be warned that on an 80-column display,  you may not see all
the data. And,  of course, if you've set MPC code 500 (geocentric), there
is no such thing as an altitude or azimuth,  and they won't be shown.

   Motions can be shown in total motion/position angle form (the
default),  or as separate RA and dec motions.  'e' toggles this.

   By default,  Find_Orb will show this sort of "observables" data.
Hitting 'c' cycles from display of observables to display of state
vectors (position and velocity in Cartesian coordinates), positions
(same thing minus the velocities),  orbital elements in MPCORB format,
elements in MPC eight-line form,  and close approaches.

   If you tell Find_Orb to show Close Approaches, it will generate the
ephemeris,  then search within it for distance minima.  As it finds them,
it will interpolate to find a time/date/distance of closest approach.
The end result will be a list of the closest approaches during that time
span.  (It's best to do this from a geocentric or heliocentric or
other-planet-centric viewpoint.)

   Any unrecognized key will get you this help text (contained in
'dosephem.txt').

MORE DETAILS ON DATE ENTRY:

   You can enter dates/times in Find_Orb in a wide variety of ways.
Essentially,  if a human can understand the input,  the program
probably will,  too.

   Examples of the most basic ways of entering time are as follows:

   YOUR INPUT             PROGRAM INTERPRETATION
------------------------  ----------------------
1997-May-6 12:30:23.3348   ( 6 MAY 1997 12:30:23.3348)
1997May-6                  ( 6 MAY 1997 00:00:00)
6 May                      ( 6 May of the current year)
12:30:23.3348              ( 12:30:23.3348 on the current date)
12:30                      ( 12:30 on the current date)

   You can separate the day/month/year with -, /, space,  or periods.
You could also use '5' instead of 'May' (though this can result in the
problems, since "5/6" can mean May 6 or 5 June;  see details below. It's
therefore recommended that you use month names.)  The program will
figure out where something like "1997may6" ought to have spaces.  (Case
is always ignored.)

   In addition to the time formats listed above,  entries such as the
following are accepted.  These either make it simpler to enter certain
times,  or allow for different common methods (Julian Day entry,  decimal
days or years,  offsetting by a particular time interval,  and so on.)

   YOUR INPUT             PROGRAM INTERPRETATION
------------------------  ----------------------
19970506 12:30:23.3348     ( 6 MAY 1997 12:30:23.3348)
970506 12:30:23.3348       (same as above)
6/18/2004                  (18 Jun 2004 00:00:00)
6.18.2004                  (same as above)
3:14.159                   (reset time to 3:14.159,  leave date alone)
13:                        (reset time to 13:00:00, leave date alone)
11/2 (or 11/f or 11 FE)    (11 Feb 00:00:00,  no change of year)
11 2 (or 11/2 or 11-2)     (same as above)
11.25 2                    (Same as above,  but 6:00:00)
11.25 2 -10m               (10 Feb  5:50:00,  ten minutes prior to above)
+6d                        (advance six days from current time)
-13.4h                     (subtract 13.4 hours from current time)
-14h +36m                  (subtract 14 hours, then add 36 minutes)
Ap                         (April of current year)
Fri                        (Friday closest to current time)
Fri+2w (or fr+14d)         (Two weeks from the nearest Friday)
7.125                      (7th of current month at 3:00)
7 :                        (7th of current month, leave time unchanged)
:43:18 (or :43.3)          (43 minutes 18 seconds, hour unchanged)
JD 2451545.                ( 1 JAN 2000 12:00 )
j2451545                   (same as above)
2451545                    (same as above)
mjd 51000                  (MJD 51000 = JD 2451000.5 = 6 Jul 2008 0:00:00)
2008-03-14T15:26:53.5      (FITS-style time: 2008 Mar 14, 15:26:53.5)
2008/50 (or 50-2008)       (50th day of 2008: 2008 Feb 19)
50 2008 3:14:15.9          (same as above, but sets time to 3:14:15.9)
50.75 2008                 (50th day of 2008,  18:00)
050.75                     (50th day of current year,  18:00)
2008 o (or Octob 2008)     ( 1 OCT 2008 00:00:00)
y1952.34                   (decimal year: about a third of the way into 1952)
1952.34                    (same as above)

   Essentially,  one can enter calendar-style dates; some special date
formats;  a day-of-year;  and one can add/subtract offsets from the time.

   Calendar-style input:  (This is all most people will need or want to
know!) You can enter a day, month, and year (or just a day and month),
optionally followed by a time of day.  The program will usually figure
out more unusual inputs,  because it can see that (for example) 1997 must
be a year, not a month or a day; or that "mar" must be a month, not a day
or year. With '5-1997-15',  for example, the input numbers can be in any
order, and the program will still recognize that this must mean 1997 May
15. A year after 31 AD, a month name,  and a day can be entered in any
order, and the program will be able to sort things out. But when given
inputs such as '3/4/5',  year/month/day is assumed.

   Month names are interpreted "logically".  For example, at least in English,
'f' is unambiguously February (no other month starts with F) and will be
recognized as such,  but 'ju' could be either June or July. In such cases,
the program will choose the first possible month,  so 'j'=January,
'JU'=June, 'Jul'=July. 'Febru' or 'f' or 'FEB' or 'february' would all be
understood to mean February.

   If a time (hours:minutes or hours:minutes:seconds) follows a date,  it's
used;  otherwise,  0:00 is assumed.  If just a ':' follows a date,  the time
is left unchanged.  The day can include a decimal portion (as some of the
above examples do).

  You can enter just a month name (as shown above) or just a number.  The
interpretation of that number will be:

One or two digits:   Reset day and decimal part of day of month
Three digits:        Reset day of year
Four or five digits: Reset year
Six-digit number:    YYMMDD.  If the year is less than 40,  it's assumed to
                     be a 21th-century year (2000 is added).  Otherwise,
                     it's assumed to be a 20th-century year (1900 is added).
Seven digits:        Julian Day
Eight-digit number:  YYYYMMDD

   So one can just enter '3',  for example,  to reset to the third of the
current month;  or '2005' to get 1 January 2005;  or '2451545' to get JD
2451545 = 1.5 January 2000.  If a year entered in this manner has a decimal
part,  you'll get that fractional part of a year added. But if you want to
set the year -23300 or 130000,  you'll need to use 'y-23300' or 'y130000';
for a JD before 1000000 or after 9999999,  you'd need to use 'j' or 'jd'
followed by the JD. Decimal parts of a day can be added,  so that
'030913.75' is equivalent to '030913 18:' is equivalent to '2003 Sep 13
18:00:00'.

   To get the output you want,  you may need to add leading zeroes. If
you wanted the fiftieth day of the current year,  for example,  you'd
use '050',  because '50' would get you the fiftieth day of the current
month (i.e.,  most of the way into the next month). '0050' would get you
the year 50, '00501007' Oct 7 of that year,  and so on.

   As shown above,  three digits (optionally followed by a decimal
portion) will be interpreted as setting that day of the year.  Also, if
you enter two numbers,  both greater than 31, the program assumes they
are the year and day of the year (thus the "2008/50" and "50 2008"
examples above).  The program assumes that the larger number is the year.

   A '+' or '-' followed by a number will add/subtract that number of days
to the current time.  One can add a letter specifying time units: 'd' (day),
'h' (hour), 'm' (minute), 's' (seconds), 'w' (weeks), 'l' (lunations), 'y'
(years), 'c' (centuries).  Some examples are shown above.

   This can be useful in dealing with time zones.  For example,  if your
default time zone is UT,  but you want to enter an Eastern US (UT-5) time,
you can just add '-5h' to it.

   You can add more than one offset;  for example,  Fri+2w -5h  would mean
"two weeks from the nearest Friday, midnight Eastern US time."

   Some other forms will be interpreted,  but if there's ambiguity,
you may not get what you wanted.

   To be added:  it would be nice if one could add 'UT' or 'EST' or 'LST'
or 'UTC-8' or similar time zone abbreviations to any of the above entries.