Source Code 1994 March/Source_Code_CD-ROM_Walnut_Creek_March_1994.iso/compsrcs/misc/volume28/ephem/part02

Text File | 1992-03-14 | 54.5 KB | 1,576 lines

Newsgroups: comp.sources.misc
From: [e-mail] (Elwood C. Downey)
Subject:  v28i085:  ephem - an interactive astronomical ephemeris, v4.28, Part02/09
Message-ID: <[e-mail]>
X-Md4-Signature: e315f154a49e96281bca55b6668366d5
Date: Tue, 10 Mar 1992 21:56:48 GMT
Approved: [e-mail]

Submitted-by: [e-mail] (Elwood C. Downey)
Posting-number: Volume 28, Issue 85
Archive-name: ephem/part02
Environment: UNIX, VMS, DOS, MAC
Supersedes: ephem-4.21: Volume 14, Issue 76-81

#! /bin/sh
# into a shell via "sh file" or similar.  To overwrite existing files,
# type "sh file -c".
# The tool that generated this appeared in the comp.sources.unix newsgroup;
# send mail to [e-mail] if you want that tool.
# Contents:  Man.txt.b nutation.c watch.c
# Wrapped by kent@sparky on Tue Mar 10 14:34:05 1992
PATH=/bin:/usr/bin:/usr/ucb ; export PATH
echo If this archive is complete, you will see the following message:
echo '          "shar: End of archive 2 (of 9)."'
if test -f 'Man.txt.b' -a "${1}" != "-c" ; then
  echo shar: Will not clobber existing file \"'Man.txt.b'\"
else
  echo shar: Extracting \"'Man.txt.b'\" \(37262 characters\)
  sed "s/^X//" >'Man.txt.b' <<'END_OF_FILE'
X
X
X
X                                       - 16 -
X
X
X     7.2.  Magnitude models
X
X     Ephem supports two different magnitude models. One, denoted here as g/k,
X     is generally used for comets and is always used for hyperbolic and
X     parabolic objects and optionally for elliptical objects. The other,
X     denoted H/G, is generally used for asteroids in the Astronomical Almanac
X     and may be used with elliptical objects.
X
X     7.2.1.  g/k model
X
X     This model requires two parameters to be specified.  One, the absolute
X     magnitude, g, is the visual magnitude of the object if it were one AU from
X     both the sun and the earth.  The other, the luminosity index, k,
X     characterizes the brightness change of the object as a function of its
X     distance from the sun. This is generally zero, or very small, for inactive
X     objects like asteroids.  The model may be expressed as:
X
X         m = g + 5*log10(D) + 2.5*k*log10(r)
X       where:
X         m = resulting visual magnitude;
X         g = absolute visual magnitude;
X         D = comet-earth distance, in AU;
X         k = luminosity index; and
X         r = comet-sun distance.
X
X     Note that this model does not take into account the phase angle of
X     sunlight.
X
X     When using this model for elliptical objects, the first of the two
X     magnitude fields must be preceded by a letter "g" in both the ephem.db
X     database file and the corresponding quick-choice elliptical object
X     definition prompt; otherwise the default magnitude model for elliptical
X     objects is the H/G model.
X
X     7.2.2.  H/G model
X
X     This model also requires two parameters. The first, H, is the magnitude of
X     the object when one AU from the sun and the earth. The other, G, attempts
X     to model the reflection characteristics of a passive surface, such as an
X     asteroid. The model may be expressed with the following code fragment:
X
X         beta = acos((rp*rp + rho*rho - rsn*rsn)/ (2*rp*rho));
X         psi_t = exp(log(tan(beta/2.0))*0.63);
X         Psi_1 = exp(-3.33*psi_t);
X         psi_t = exp(log(tan(beta/2.0))*1.22);
X         Psi_2 = exp(-1.87*psi_t);
X         m = H + 5.0*log10(rp*rho) - 2.5*log10((1-G)*Psi_1 + G*Psi_2);
X       where:
X         m   = resulting visual magnitude
X         rp  = distance from sun to object
X         rho = distance from earth to object
X         rsn = distance from sun to earth
X
X     Note that this model does not take into account the phase angle of
X
X
X
X
X
X
X
X
X
X                                       - 17 -
X
X
X     sunlight.
X
X     This is the default magnitude model for elliptical objects but it can also
X     be explicitly indicated when the first of the two magnitude fields is
X     preceded by a letter "H" in both the ephem.db database file and the
X     corresponding quick-choice elliptical object definition prompt.
X
X     7.3.  Database File
X
X     You may save a list of objects in a file to be used for setting OBJX and
X     OBJY. The default name of this file is ephem.db. You may also set it from
X     the command line with the -d option, or set it with the EPHEMDB
X     environment variable.
X
X     The file consists of one object per line.  All lines that do not begin
X     with an alpha character are ignored and may be used for comments.  Each
X     line contains several fields, each separated by a comma.  The first field
X     is the name of the object.  The second field is the type of the object,
X     that is, one of the strings "fixed", "elliptical", "hyperbolic" or
X     "parabolic"; actually, "f", "e", "h" and "p" are sufficient.  The
X     remaining fields depend on the type of object.  They are exactly the same
X     parameters, and in the same order, as ephem asks for when defining the
X     object from the menu.  The size field is last and is optional for
X     compatibility with older versions.
X
X     8.  Plotting
X
X     Each time a field is drawn on the screen during a full screen update cycle
X     (that as, during automatic looping or a manual "q" command character from
X     the main menu but not from a screen redraw from control-l or when an
X     individual planet is turned on or a single time field is changed) its
X     full-precision value may be written to a file.  This implies you may not
X     plot a field from other than the current menu at the time plotting is on.
X     You can append several plot runs together, however, if necessary.
X
X     Each line in the file consists of a tag character followed by two or three
X     floating point variables, all separated by commas. If there are two
X     values, they should be interpreted to be x and y (or perhaps r and theta).
X     If there is a third, it is a z or trace value.
X
X     For efficiency on systems that can compute a screen full faster than they
X     can display it, screen updates are suppressed while plotting is on and
X     NStep is greater than 1. This can greatly reduce the time to generate a
X     long plot file. Fields are still logged for plotting; they just are not
X     drawn on the screen.
X
X     The Plot field controls plotting.  Whether plotting is currently active is
X     indicated by "on" or "off" immediately to its right.
X
X     Picking "Plot" brings up a quick-choice menu, as follows:
X
X     Select: Select fields, Display a plot file, Cartesian coords, Begin plotting
X
X
X
X
X
X
X
X
X
X
X
X                                       - 18 -
X
X
X     8.1.  Defining plot fields
X
X     Select the "Select fields" option.  You will be asked to move the cursor
X     to the field you want to use as the x coordinate (abscissa), then asked to
X     choose the y coordinate (ordinate), then asked to choose an optional z
X     trace variable and finally a tag character.  (Of course, you may have in
X     mind fields that are more appropriately displayed in other than Cartesian
X     coordinates, in which case think of x, y and z as dimensions.) If you type
X     q for either x or y then no more fields will be defined.  If you type q
X     for the z field there will be no z field.  You can not label a plot line
X     with the letter "q" at this time.
X
X     This then repeats so you may choose up to ten of these sets for any given
X     plot run.  Each set defines what will become a line on the final plot.
X     Note that you may select the "Search" field to indicate use of the current
X     search function; that function must be defined by the time plotting is
X     turned on.
X
X     If you turn plotting off and back on the fields selected for plotting are
X     reactivated the same as they were last time. You may change them if
X     desired, of course, but there is no need to redefine them if you do not
X     wish to change them.
X
X     8.2.  Displaying a plot file
X
X     Select the "Display a plot file" option to generate a crude plot on the
X     screen of an existing plot file previously created by ephem.  The entries
X     in the file will be drawn on the screen using their tag characters; the
X     plot remains on the screen until you type any character.
X
X     The plot may be made in polar or Cartesian coordinates, depending on the
X     setting of the plotting mode in the quick-choice (see next section).
X
X     8.3.  Cartesian or Polar coords
X
X     This toggles the plotting mode coordinate system.  The mode remains until
X     changed.  Polar coordinates assume the first numeric field in the plot
X     file is the radius, and the second is the angle counterclockwise from
X     right, in degrees.
X
X     8.4.  Begin Plotting
X
X     If plot field lines are defined then the third option, "Begin plotting"
X     will be available.  You will be asked for the name of the file to use.  If
X     it already exists you will be asked whether to overwrite it or append to
X     it.  You will also be asked for a title line that will become the next
X     line of the file, automatically prefixed with a "*" to make it a comment
X     line.  Once you have chosen a file, plotting is on and the top menu
X     plotting status field changes to "on".  The default plot file name is
X     ephem.plt.  The values are written to the plot file each time they are
X     updated on the screen until you select "Plot" again and select the "Stop"
X     option to turn plotting back off.
X
X
X
X
X
X
X
X
X
X
X
X                                       - 19 -
X
X
X     8.5.  Stopping Plotting
X
X     If plotting is on, then selecting the Plot field in the top section will
X     turn plotting off. You may pick Plot again and resume with the same fields
X     by selecting "Begin plotting" again.
X
X     Note that due to internal buffering the plot file will not be completely
X     written to disk until plotting is turned off.
X
X     9.  Listing
X
X     This feature works very much like Plotting. However, the fields you select
X     define columns of a table generated as ephem runs. These columns are look
X     exactly like their corresponding fields on the ephem screen and so are far
X     more readable than plot files.
X
X     See the section on Plotting for an explanation of the quick-choice menu.
X     The general operation is very much the same.
X
X     10.  Watching
X
X     You may generate a simple drawing on the screen of the local sky in two
X     forms or the solar system by selecting "Watch".  It will bring up a
X     quick-choice menu as follows:
X
X     Select: Sky dome, Alt/az sky, Solar system, No trails
X
X
X     10.1.  Trails
X
X     You may either erase after each iteration or leave the tags up, referred
X     to as "trails". Picking the right-most choice will toggle between "No
X     trails" and "Leave trails"; you should set it as desired before you select
X     the style of sky plot you wish.  Ephem will remember your selection.
X
X     10.2.  Sky dome
X
X     This draws the currently active planets within a circle that represents
X     the locally visible hemisphere.  This is similar to the formats commonly
X     used in the popular astronomy magazines.  East is left, south is down,
X     west is right and north is up.
X
X     10.3.  Alt/az sky
X
X     This is a cylindrical projection showing the currently active planets as
X     they would appear in the sky looking southwards at the current time and
X     date.  The coordinate system is such that 0 degrees azimuth (north)
X     through 360 degrees (north, once around) is mapped to the horizontal
X     screen dimension, and 0 degrees altitude (level) through 90 degrees (the
X     zenith) is mapped to the vertical dimension. Thus, the bottom row is the
X     horizon and all across the top is the zenith.
X
X
X
X
X
X
X
X
X
X
X
X
X                                       - 20 -
X
X
X     10.4.  Solar System
X
X     This selection draws the currently active planets as they would appear
X     looking "down from the top" of the ecliptic, with the sun at the center
X     and zero hours right ascension towards the right.  The scale is adjusted
X     to roughly fill the screen according to the outer-most active planet.
X     Note that the scaling does not take into account the distances of the user
X     defined objects so, if they don't appear, select a planet that is at least
X     as far out as they are.  The screen transformation assumes a screen aspect
X     width/height ratio of 4/3.  Down the left column of the screen is the
X     heliocentric altitude of the planet above or below the ecliptic, drawn to
X     the same scale as the circular display.  Values so close as to land on the
X     same line are sorted left to right; the S and E symbols always denote
X     heliocentric altitude 0.
X
X     In each style of display, pressing RETURN advances the time by whatever
X     amount StpSz is set to.  Pressing "h" advances the time by one hour, "d"
X     advances by one day, and "w" advances by one week (seven days).  Pressing
X     "q" returns to the watch quick-choice menu from which you may select
X     another display style or return to the main tabular display by typing
X     another "q".  Pressing any other key starts an automatic loop with each
X     step advancing by StpSz; pressing any key stops the looping.
X
X     As symbols are placed, collisions (overstrikes) are avoided by moving
X     characters in such a way as to maintain increasing sorted order towards
X     the right.
X
X     When you return to the main menu, the last watched time will be maintained
X     as the current time.  The StpSz is not changed.
X
X     11.  Searching
X
X     Ephem can search for arbitrary conditions to exist among most displayed
X     fields.  You first enter a function, then select from among three forms of
X     equation solvers to iteratively solve for the next time when the function
X     meets the requirements of the solver. The solver selects the next time for
X     which it wants the function evaluated and sets StpSz so that the next
X     iteration will occur at that time. The solvers continue to iterate until
X     either they achieve their goal or NStep reaches 0.
X
X     You may set NStep to be quite large and let ephem search unattended or set
X     it to 1 and watch it converge one step at a time. You may also plot at the
X     same time as search to record the exact steps ephem took to converge.
X     (But recall that screen updates are suppressed if plotting is also on).
X
X     The "Search" selection in the top half of the screen controls all
X     searching.  Picking it brings up a quick-choice menu as follows:
X
X     Select: Find extreme, Find 0, Binary, New function, Accuracy
X
X
X     11.1.  Find extreme
X
X     This search algorithm searches for a local maximum or a minimum in the
X
X
X
X
X
X
X
X
X
X                                       - 21 -
X
X
X     search function, whichever it finds first. It begins by evaluating the
X     search function at the current time then for two more times each separated
X     by StpSz. It then fits these three points to a parabola and solves it for
X     the time of its maximum (or minimum). StpSz is set so that the next
X     iteration will evaluate at this point.  This parabolic fit solution keeps
X     repeating until StpSz changes by less than the desired accuracy or until
X     the curve becomes so flat that an extrema appears too broad to find.
X
X     11.2.  Find 0
X
X     This search algorithm uses the secant method to solve for the time at
X     which the search function is zero. The function is evaluated at the
X     current time and then again StpSz later to establish a slope for which the
X     x-intercept is found as the next zero guess. This is used to set StpSz for
X     the next desired time value and the slope hunting process repeats until
X     StpSz changes by less than the desired accuracy.
X
X     11.3.  Binary
X
X     This search algorithm must be used with a search function that yields a
X     boolean result, ie, a true or false value. The idea is that the function
X     is assumed to be one truth value when evaluated at the present time, and
X     the opposite truth value when it is evaluated StpSz later. The algorithm
X     will then do a binary search for the time when the truth value changes.
X
X     The binary algorithm does not begin until the state change is bounded in
X     time.  Initially, as long as the truth value at StpSz is the same as the
X     previous value the algorithm will just keep moving in time by StpSz
X     looking for when the state changes.  That is, a linear search is initiated
X     to bound the state change, then the binary search proceeds.
X
X     11.4.  Define a New function
X
X     Select "New function" to display the current search function.  If you type
X     "q" it will be left unchanged.  If you type RETURN it will be erased.  If
X     you type anything else it will be compiled and, if there are no errors, it
X     will become the new search function.  Once a valid function has been
X     stored, it will remain unless changed.  If a search function is selected
X     and there is as yet no valid search function defined, you will
X     automatically be asked to enter one as though you had selected "New
X     function."
X
X     A search function consists of intrinsic functions, field-specifiers,
X     constants and operators, and precedence may be overridden with
X     parentheses.
X
X
X     11.4.1.  Intrinsic functions
X
X     In this release, the only intrinsic functions available are abs(), which
X     returns the absolute value of its argument, and sqrt(), which returns the
X     square root of its argument.
X
X
X
X
X
X
X
X
X
X
X
X                                       - 22 -
X
X
X     11.4.2.  Field Specifiers
X
X     A field in the bottom half of the menu is generally specified in the form
X     of "object_name.column_name". The object_name is enough of the planet or
X     moon name to be unique.  Use "x" or "y" for the user-specified object X or
X     Y.  The column_name is from the following table, depending on which menu
X     is up. In all cases additional characters may be entered but are ignored.
X     Also, you may use x, y and z to specify those columns of the Galilean
X     moons menu.
X
X     Planet Data Menu        Rise/Set Menu               Separation Menu
X     ------------------      --------------------        ---------------
X     al      Alt             hr      Hrs Up, or          j       Jup
X     az      Az              hu      Hrs Up              ma      Mars
X     d       Dec             raz     Rise Az             me      Merc
X     ed      Ea Dst          rt      Rise Time           mo      Moon
X     el      Elong           saz     Set Az              n       Nep
X     hla     Helio Lat       st      Set Time            pl      Pluto
X     hlo     Helio Long      ta      Transit Alt         sa      Saturn
X     ph      Phs             tt      Transit Time        su      Sun
X     ra      R.A.                                        u       Uranus
X     sd      Sn Dst                                      ve      Venus
X     si      Size
X     vm      VMag
X
X
X     A few fields do not use this "dot" notation.  The following top-half
X     fields are indicated using these codes:
X
X     da      Dawn
X     du      Dusk
X     n       NiteLn
X
X
X     Use "jI" and "jII" to indicate one of the two rotational systems of
X     Jupiter's central meridian longitude.
X
X     Remember, searching may only involve fields being calculated for display
X     at the time the solver is active.  While you can syntactically include any
X     field in a search function it is useless to define a search that uses
X     fields from other than the menu that is selected at the time the search is
X     running.
X
X     11.4.3.  Constants
X
X     Constants may be integers or floating point numbers. The latter may be
X     expressed in scientific notation if desired. Examples include 100, .9,
X     1.234, 1e10 and 1.2e-4.  Any number may be preceded by - to make it
X     negative.
X
X     11.4.4.  Operators
X
X     The collection of arithmetic, relational and boolean operators provided
X     mimics those of C language as listed in the following table, in decreasing
X
X
X
X
X
X
X
X
X
X                                       - 23 -
X
X
X     order of precedence.  Operators grouped together have the same precedence
X     and all have left-to-right associativity. Parentheses may be used as
X     desired.
X
X     Symbol  Meaning                 Resulting type
X     ------  --------------------    --------------
X     *       multiply                arithmetic
X     /       divide                  arithmetic
X
X     +       add                     arithmetic
X     -       subtract                arithmetic
X
X     >       greater than            boolean
X     >=      greater than or equal   boolean
X     <       less than               boolean
X     <=      less than or equal      boolean
X
X     ==      equality                boolean
X     !=      inequality              boolean
X
X     &&      logical and             boolean
X
X     ||      logical or              boolean
X
X
X     11.5.  Specifying Search Accuracy
X
X     Selecting "Accuracy" allows you to specify when the search will stop.  The
X     search algorithms will stop when StpSz becomes equal to or less than this
X     value. The default is one minute.  If ephem has not yet converged to the
X     specified accuracy but NStep has decremented to 1, the searching will stop
X     but the search status field will still indicate which search procedure is
X     in effect. To try more iterations you may increase NStep and resume
X     searching. If the accuracy was achieved, the search status field will
X     switch to "off" with the number of "unused" steps remaining in NStep and
X     the last step size in the StpSz fields.
X
X     11.6.  Stop
X
X     If searching is on, this option will also appear on the quick-choice menu
X     and may be selected to turn off the search.
X
X     11.7.  Example Searches
X
X     As an example, let's find when Pluto again becomes the furthest planet
X     from Sol.  You may find when the difference in their sun distance is zero,
X     or you might use a binary search on the condition that Pluto's sun
X     distance is larger then Neptune's.
X
X     To try the former approach select Search, select "Find 0", specify the
X     search function to be:
X
X     pl.sd - nep.sd
X
X
X
X
X
X
X
X
X
X
X                                       - 24 -
X
X
X     set StpSz to something large like 10d, NStep to allow several iterations
X     like 20, and then type "q" to start the search and watch ephem do the
X     hunt.  Ephem will settle on about 21:02 1/10/1999 UT.
X
X     To try a binary search, you first need to have some idea of when the event
X     will occur so you can eliminate the initial linear search for the state
X     change. We can start at, say, 1/1/1999, set StpSz to 30d, select Binary
X     search, specify the search function to be:
X
X     pl.sd > nep.sd
X
X     and go. Once it brackets the state change note how StpSz keeps being cut
X     in half but can go in either direction (sign) as it divides each interval
X     in half.  Ephem will converge on the same answer.
X
X     11.8.  Another Example
X
X     To find the time of last quarter moon during December, 1989, use the "Find
X     0" search algorithm to solve "moon.el + 90".  (At last quarter, the moon
X     is 90 degrees west of the sun, or -90 east in ephem's elongation display.)
X     Set the initial time to mid-month, 12/15/1989, StpSz to 1 day and NStep to
X     10. Ephem takes only a few iterations to settle on 23:57 12/19 UT.
X
X     11.9.  Caution
X
X     Beware that most celestial phenomena are generally pseudo-periodic in
X     nature.  In early search steps ephem can easily skip over a local maxima
X     and find a later one, which, while correct, may not be what was desired.
X     In general, the closer you can be when you start the search the better
X     ephem can refine it; it is not as good with very broad searches that can
X     go "wild". Set StpSz large enough to offer significant change in the
X     function value, but small enough not to skip too far.
X
X     For example, Saturn and Neptune had three close approaches during 1989.
X     If you did not know this then just asking ephem to find a minimum would
X     have produced different results depending on the starting conditions.
X     When starting a search for a certain class of event it is a good idea to
X     first use the plotting or watching facility of ephem to get a broad
X     picture of the general circumstances then use ephem's search facility to
X     refine a given region (or create and inspect a plot file and do your own
X     interpolation directly from it separately).
X
X     Similarly, ephem's searching techniques are not good for eclipses because
X     the moon and sun are close every month; the trick is sorting through the
X     frequent conjunctions for ones that are particularly close. One needs a
X     way of establishing an envelope fit to the local extrema of a cyclic
X     function in order to find a more global extreme.
X
X     12.  Implementation Notes
X
X     Remember that everything is for the current local time and day. So, for
X     example, the calendar marks moon events in local time; commercial
X     calendars usually mark the UT date.  Similarly, the rise/set times are for
X     the current local day.
X
X
X
X
X
X
X
X
X
X                                       - 25 -
X
X
X     The program uses a horizontal plane tangent to the earth as the horizon
X     for all altitude calculations, rise/set events, etc.  This is not the same
X     as the angle up from the local horizon unless the observer is directly on
X     the ground due to earth's curvature.  The effect can be found from:
X
X             sin(a)**2 = (h**2 + 2Rh) / (R+h)**2
X         where:
X             R = radius of earth
X             h = height above ground (same units as R)
X             a = increase in altitude
X
X     For example, the effect is more than two arc minutes at a height of 5
X     feet.
X
X     Visual magnitudes are not very accurate ... I haven't bothered to fix.
X
X     The accuracy of ephem can not be specifically stated since the Duffett-
X     Smith book does not warrant its planet position polynomials to any given
X     degree. I know for sure that better accuracy could be achieved if ephem
X     used TDT but I have not yet decided on a suitable algorithm.  Allowing for
X     this manually, (see the Wish List section) comparisons with the
X     Astronomical Almanac are often within a few arcseconds.
X
X     The program uses double precision throughout. While this precision might
X     seem a little ridiculous, it is actually more efficient for most
X     traditional K&R C compilers and the search functions seem to be are far
X     more stable.
X
X     Searching and plotting always use full precision but if neither of these
X     are turned on pure display and watching only recompute a given planets new
X     location if the time has changed enough to effect the required display
X     precision, based on the planets mean apparent orbital motion.
X
X     The sun-moon distance is the solution for the third side of a planar
X     triangle whose two other sides are the earth-moon distance and earth-sun
X     distance separated by the angle of elongation.
X
X     Beware of computing with the user-defined objects before they are properly
X     defined.
X
X     If a floating point exception occurs ephem will stop further computations
X     on the current screen update and stop any automatic looping.
X
X     12.1.  Program limits
X
X     The search function is limited to a maximum of 32 instructions (each
X     constant, field spec, and operation is one instruction), with no more than
X     a total of 16 constants and field specs. At run time, the function can not
X     require more than 16 stacked values (due to operator precedence or
X     explicit parenthetical expressions) to evaluate.
X
X     No more than 32 different fields can be tracked simultaneously for
X     plotting and/or searching.
X
X
X
X
X
X
X
X
X
X
X                                       - 26 -
X
X
X     No more than 10 lines may be plotted at once.
X
X     The maximum file name length is 14 characters.
X
X     13.  DOS Installation Procedure
X
X     You must be running DOS V2.0 or later, though somewhere between V2.0 and
X     V3.21 the behavior of control-c to terminate the program was fixed.  An
X     8087 floating point chip will be used if present.
X
X     The distribution floppy contains five files:
X     README describes last minute items and details of this release.
X     MAN.TXT is this manual, hopefully formatted and printable on most any
X     printer.
X     EPHEM.EXE is the executable program.
X     EPHEM.CFG is a sample configuration file.
X     EPHEM.DB is a sample database.
X     To run the program, make working copies of these files in a directory and
X     run "ephem" from that directory.
X
X     13.1.  Setting TZ
X
X     Before running ephem, you should set a DOS environment variable, TZ.  It
X     is is used to establish the timezone name and hours offset whenever the
X     "Now" shorthand is used from ephem, either from the configuration startup
X     file or whenever any time field is changed manually.  Set it in the
X     following form:
X
X          set TZ=SSSnDDD
X
X     where
X
X     SSS  is the 3-letter abbreviation for the local standard timezone;
X
X     n    is a number between -23 to 24 indicating the number of hours that are
X          subtracted from GMT to obtain local standard time;
X
X     DDD  is an optional 3-letter abbreviation for the local daylight savings
X          time zone name. Leave it off if you do not have savings time in your
X          area or it is not currently in effect. If the changeover dates differ
X          from the internal algorithm, just use SSS and n directly.
X
X     For example, in the midwestern United States with savings times set
X     TZ=CST6CDT
X
X     If for some reason your system does not change to savings time at the
X     right time, then omit the DDD parameter and just set the SSS and n to
X     exactly what you want.
X
X     You can put this in your AUTOEXEC.BAT file so it gets set each time you
X     boot DOS.
X
X
X
X
X
X
X
X
X
X
X
X
X                                       - 27 -
X
X
X     14.  Known Bugs and Wish List
X
X     incorporate Terrestrial Dynamical Time (known as Ephemeris Time prior to
X     1984).  TDT is about 57 seconds ahead of UT1 in 1990.
X
X     it's too easy to turn on objx/y before it's defined and bomb out.
X
X     add explicit searching for eclipses and occultations.
X
X     in watch mode, RTC reverts back to being based off the time when watch was
X     first entered.
X
X     add a facility (or tool) to find g/k from a set of observed magnitudes.
X
X     add search criteria and a screen-based selection mechanism for database
X     objects.
X
X     add plot options to reverse x and/or y direction and add some tick marks.
X
X     continue pursuit of moon and other information for other planets.
X
X     add shorthands for some sidereal and synodic step sizes.
X
X     the built-in elements for pluto need to be updated. the elements for pluto
X     in the included ephem.db database sampler are more accurate.
X
X     plotting or listing rise/set that doesn't happen just reshows the last
X     entry.
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X                                       - 28 -
X
X
X     15.  Sample Screens
X
X     Here are sample ephem screens. They are generated using the first sample
X     ephem.cfg file (listed in the section describing the configuration file).
X     There is one for each of the possible screen formats.  The rise/set screen
X     was done using the Adaptive option.  The separations screen was done using
X     the Topocentric option.
X
X
X
XMove to another field, RETURN to change this field, ? for help, or q to run
X
XCDT 19:00:00  4/30/1990 | LST    8:19:50 | Lat   44:50:37 |      April 1990
XUTC  0:00:00  5/01/1990 |                | Long  93:42:08 | Su Mo Tu We Th Fr Sa
XJulianDat 2448012.50000 | Dawn      4:10 | Elev    800 ft |  1  2  3  4  5  6  7
XWatch                   | Dusk     22:15 | Temp      40 F |  8 FM 10 11 12 13 14
XListing             off | NiteLn    5:55 | AtmPr 29.50 in | 15 16 17 18 19 20 21
XSearch              off |                | TZ     5:00:00 | 22 23 NM 25 26 27 28
XPlot                off | NStep        1 | Epoch   2000.0 | 29 30
XMenu        Planet Data | StpSz RT CLOCK | Pause        0 |
X--------------------------------------------------------------------------------
XOCX  R.A.    Dec    Az     Alt  H Long H Lat  Ea Dst Sn Dst Elong  Size VMag Phs
XSu  2:32.3  14:58 278:40  12:38 220:22        1.0075               1905  -27
XMo  8:09.9  21:11 186:06  65:53 119:55   1:04 234821 1.0071   79.5 1897  -12  44
XMe  2:49.4  17:39 277:48  17:26 214:08   1:43 0.5764 0.4360    4.9 11.7  1.6   1
XVe 23:49.4  -2:25 296:53 -27:39 282:39  -1:30 0.9288 0.7276  -43.9 18.2 -4.8  64
XMa 22:39.8 -10:09 308:17 -44:14 297:56  -1:43 1.5438 1.4067  -62.9  6.1  0.3  89
XJu  6:30.9  23:23 235:13  59:04 106:16   0:08 5.6806 5.1941   56.6 34.6 -2.0  99
XSa 19:49.6 -20:53  17:24 -65:14 289:45   0:10 9.7077 10.017 -105.0 17.1  1.1 100
XUr 18:41.9 -23:24  51:18 -60:39 276:55  -0:18 18.864 19.401 -120.9  3.5  5.6 100
XNe 19:03.2 -21:46  40:51 -62:01 282:48   0:51 29.754 30.207 -115.8  2.1  7.9 100
XPl 15:14.8  -1:26  81:18 -10:37 226:18  15:28 28.693 29.658 -162.9  0.3 13.6 100
XX   0:08.3  36:01 316:59   5:58 238:20  26:29 0.5622 0.6657  -38.4  0.0  1.5  33
XY  15:22.9  -2:40  80:43 -12:54 226:17  10:49 2.3635 3.3381 -162.5  0.0 10.1100
X
X
X
X
X
X
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X
X
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X
X
X
X
X
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X
X
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X
X
X
X
X
X
X
X
X                                       - 29 -
X
X
XMove to another field, RETURN to change this field, ? for help, or q to run
X
XCDT 19:00:00  4/30/1990 | LST    8:19:50 | Lat   44:50:37 |      April 1990
XUTC  0:00:00  5/01/1990 |                | Long  93:42:08 | Su Mo Tu We Th Fr Sa
XJulianDat 2448012.50000 | Dawn      4:10 | Elev    800 ft |  1  2  3  4  5  6  7
XWatch                   | Dusk     22:15 | Temp      40 F |  8 FM 10 11 12 13 14
XListing             off | NiteLn    5:55 | AtmPr 29.50 in | 15 16 17 18 19 20 21
XSearch              off |                | TZ     5:00:00 | 22 23 NM 25 26 27 28
XPlot                off | NStep        1 | Epoch   2000.0 | 29 30
XMenu      Rise/Set Info | StpSz RT CLOCK | Pause        0 |
X--------------------------------------------------------------------------------
XOCX Rise Time    Rise Az  Trans Time  Trans Alt  Set Time    Set Az    Hours Up
XSu     6:05       67:48     13:12       60:01     20:20      292:28     14:15
XMo    10:54       57:14     18:49       66:01      1:56      304:46     15:02
XMe     6:13       63:34     13:30       62:51     20:47      296:04     14:34
XVe     4:35       93:02     10:29       42:33     16:23      267:14     11:48
XMa     3:57      103:53      9:20       34:52     14:43      256:17     10:45
XJu     9:24       54:59     17:11       68:33      1:00      305:01     15:36
XSa     1:56      119:18      6:31       24:17     11:06      240:42      9:10
XUr     1:01      123:08      5:24       21:47      9:46      236:52      8:45
XNe     1:14      120:39      5:45       23:24     10:16      239:21      9:02
XPl    19:55       91:11      1:57       43:46      7:55      268:48     12:00
XX      1:41       32:26     10:51       81:10     20:00      327:20     18:19
XY     20:08       92:55      2:06       42:29      7:59      267:01     11:50
X
X
X
XMove to another field, RETURN to change this field, ? for help, or q to run
X
XCDT 19:00:00  4/30/1990 | LST    8:19:50 | Lat   44:50:37 |      April 1990
XUTC  0:00:00  5/01/1990 |                | Long  93:42:08 | Su Mo Tu We Th Fr Sa
XJulianDat 2448012.50000 | Dawn      4:10 | Elev    800 ft |  1  2  3  4  5  6  7
XWatch                   | Dusk     22:15 | Temp      40 F |  8 FM 10 11 12 13 14
XListing             off | NiteLn    5:55 | AtmPr 29.50 in | 15 16 17 18 19 20 21
XSearch              off |                | TZ     5:00:00 | 22 23 NM 25 26 27 28
XPlot                off | NStep        1 | Epoch   2000.0 | 29 30
XMenu        Separations | StpSz RT CLOCK | Pause        0 |
X--------------------------------------------------------------------------------
XOCX Sun  Moon   Merc  Venus  Mars   Jup    Sat  Uranus  Nep  Pluto    X     Y
XSu        79:32   4:52 43:59  62:55 56:31   105:  121:   116:  163:  38:21  162:
XMo  79:32        74:49  124:   142: 23:01   175:  160:   164:  106:  99:52  108:
XMe   4:52 74:49        48:43  67:39 51:50   110:  126:   121:  163:  39:57  163:
XVe  43:59  124:  48:43        18:56  100:  61:09 77:00  71:58  129:  38:49  126:
XMa  62:55  142:  67:39 18:56         119:  42:14 58:04  53:04  111:  50:48  108:
XJu  56:31 23:01  51:50  100:   119:         162:  177:   172:  128:  80:40  130:
XSa   105:  175:   110: 61:09  42:14  162:        15:52  10:50 69:37  83:36 67:17
XUr   121:  160:   126: 77:00  58:04  177:  15:52         5:11 54:43  97:18 52:21
XNe   116:  164:   121: 71:58  53:04  172:  10:50  5:11        59:06  92:24 56:46
XPl   163:  106:   163:  129:   111:  128:  69:37 54:43  59:06         125:  2:22
XX   38:21 99:52  39:57 38:49  50:48 80:40  83:36 97:18  92:24  125:         124:
XY    162:  108:   163:  126:   108:  130:  67:17 52:21  56:46  2:22   124:
X
X
X
X
X
X
X
X
X
X
X
X
X                                       - 30 -
X
X
XMove to another field, RETURN to change this field, ? for help, or q to run
X
XCDT 19:00:00  4/30/1990 | LST    8:19:50 | Lat   44:50:37 |      April 1990
XUTC  0:00:00  5/01/1990 |                | Long  93:42:08 | Su Mo Tu We Th Fr Sa
XJulianDat 2448012.50000 | Dawn      4:10 | Elev    800 ft |  1  2  3  4  5  6  7
XWatch                   | Dusk     22:15 | Temp      40 F |  8 FM 10 11 12 13 14
XListing             off | NiteLn    5:55 | AtmPr 29.50 in | 15 16 17 18 19 20 21
XSearch              off |                | TZ     5:00:00 | 22 23 NM 25 26 27 28
XPlot                off | NStep        1 | Epoch   2000.0 | 29 30
XMenu        Jupiter Aux | StpSz RT CLOCK | Pause        0 |
X--------------------------------------------------------------------------------
X
X     Central Meridian Longitude (degs):   337.545 (Sys I)  267.021 (Sys II)
X               (GRS is at approximately 30 degs in System II)
X
X                                        Jupiter Radii
X                            X (+E)         Y (+N)      Z (+towards)
X        I   Io               0.950         -0.181         -5.808
X        II  Europa          -4.052          0.261          8.384
X        III Ganymede        -8.502          0.385         12.350
X        IV  Callisto        26.029          0.160          5.119
X
X                           G     E     JI                                    C
X West                                                                     East
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
END_OF_FILE
  if test 37262 -ne `wc -c <'Man.txt.b'`; then
    echo shar: \"'Man.txt.b'\" unpacked with wrong size!
  fi
  # end of 'Man.txt.b'
fi
if [ -f Man.txt.a ]
then
        echo adding Man.txt.b to Man.txt.a to form Man.txt
        cat Man.txt.a Man.txt.b > Man.txt
        echo removing Man.txt.a and Man.txt.b
        rm Man.txt.a Man.txt.b
fi
if test -f 'nutation.c' -a "${1}" != "-c" ; then
  echo shar: Will not clobber existing file \"'nutation.c'\"
else
  echo shar: Extracting \"'nutation.c'\" \(2011 characters\)
  sed "s/^X//" >'nutation.c' <<'END_OF_FILE'
X#include <stdio.h>
X#include <math.h>
X#include "astro.h"
X
X/* given the modified JD, mjd, find the nutation in obliquity, *deps, and
X * the nutation in longitude, *dpsi, each in radians.
X */
Xnutation (mjd, deps, dpsi)
Xdouble mjd;
Xdouble *deps, *dpsi;
X{
X    static double lastmjd = -10000, lastdeps, lastdpsi;
X    double ls, ld;    /* sun's mean longitude, moon's mean longitude */
X    double ms, md;    /* sun's mean anomaly, moon's mean anomaly */
X    double nm;    /* longitude of moon's ascending node */
X    double t, t2;    /* number of Julian centuries of 36525 days since
X             * Jan 0.5 1900.
X             */
X    double tls, tnm, tld;    /* twice above */
X    double a, b;    /* temps */
X
X    if (mjd == lastmjd) {
X        *deps = lastdeps;
X        *dpsi = lastdpsi;
X        return;
X    }
X
X    t = mjd/36525.;
X    t2 = t*t;
X
X    a = 100.0021358*t;
X    b = 360.*(a-(long)a);
X    ls = 279.697+.000303*t2+b;
X
X    a = 1336.855231*t;
X    b = 360.*(a-(long)a);
X    ld = 270.434-.001133*t2+b;
X
X    a = 99.99736056000026*t;
X    b = 360.*(a-(long)a);
X    ms = 358.476-.00015*t2+b;
X
X    a = 13255523.59*t;
X    b = 360.*(a-(long)a);
X    md = 296.105+.009192*t2+b;
X
X    a = 5.372616667*t;
X    b = 360.*(a-(long)a);
X    nm = 259.183+.002078*t2-b;
X
X    /* convert to radian forms for use with trig functions.
X     */
X    tls = 2*degrad(ls);
X    nm = degrad(nm);
X    tnm = 2*nm;
X    ms = degrad(ms);
X    tld = 2*degrad(ld);
X    md = degrad(md);
X
X    /* find delta psi and eps, in arcseconds.
X     */
X    lastdpsi = (-17.2327-.01737*t)*sin(nm)+(-1.2729-.00013*t)*sin(tls)
X           +.2088*sin(tnm)-.2037*sin(tld)+(.1261-.00031*t)*sin(ms)
X           +.0675*sin(md)-(.0497-.00012*t)*sin(tls+ms)
X           -.0342*sin(tld-nm)-.0261*sin(tld+md)+.0214*sin(tls-ms)
X           -.0149*sin(tls-tld+md)+.0124*sin(tls-nm)+.0114*sin(tld-md);
X    lastdeps = (9.21+.00091*t)*cos(nm)+(.5522-.00029*t)*cos(tls)
X           -.0904*cos(tnm)+.0884*cos(tld)+.0216*cos(tls+ms)
X           +.0183*cos(tld-nm)+.0113*cos(tld+md)-.0093*cos(tls-ms)
X           -.0066*cos(tls-nm);
X
X    /* convert to radians.
X     */
X    lastdpsi = degrad(lastdpsi/3600);
X    lastdeps = degrad(lastdeps/3600);
X
X    lastmjd = mjd;
X    *deps = lastdeps;
X    *dpsi = lastdpsi;
X}
END_OF_FILE
  if test 2011 -ne `wc -c <'nutation.c'`; then
    echo shar: \"'nutation.c'\" unpacked with wrong size!
  fi
  # end of 'nutation.c'
fi
if test -f 'watch.c' -a "${1}" != "-c" ; then
  echo shar: Will not clobber existing file \"'watch.c'\"
else
  echo shar: Extracting \"'watch.c'\" \(12217 characters\)
  sed "s/^X//" >'watch.c' <<'END_OF_FILE'
X/* these functions allow you to watch the sky or the solar system via a
X * simple character-graphics representation on the screen.
X * the interaction starts by using the current time. then control with
X *    END returns to table form; or
X *    RETURN advances time by one StpSz; or
X *    h advances once by 1 hour; or
X *    d advances once by 24 hours (1 day); or
X *    w advances once by 7 days (1 week); or
X *    any other key free runs by StpSz until any key is hit.
X */
X
X#include <stdio.h>
X#include <math.h>
X#include "astro.h"
X#include "circum.h"
X#include "screen.h"
X
X#define    SSZCOL    1        /* column to show solar system z coords */
X#define    PARK_ROW    1    /* cursor park loc after each screen */
X#define    PARK_COL    NC    /* cursor park loc after each screen */
X
X#define    DOMESKY        0    /* flags for watch_sky() */
X#define    ALTAZSKY    1    /* flags for watch_sky() */
X
X#define    SKYACC    3600.    /* desired sky plot accuracy, in arc seconds */
X#define    SSACC    3600.    /* desired solar system plot accuracy, in arc secs */
X
X/* macros to convert row(col) in range 1..NR(1..NC) to fraction in range 0..1 */
X#define    NEARONE        0.9999999
X#define    r2fr(r)        (((r)-1)/(NEARONE*NR)+1/NC/2)
X#define    c2fc(c)        (((c)-1)/(NEARONE*NC)+1/NC/2)
X#define    fr2r(fr)    ((int)((fr)*(NEARONE*NR))+1)
X#define    fc2c(fc)    ((int)((fc)*(NEARONE*NC))+1)
X
X/* single-character tag for each body.
X * order must match the #defines in astro.h and screen.h additions.
X */
Xstatic char body_tags[] = "evmjsunpSMxy";
X
X/* multiple and single loop prompts */
Xstatic char frprompt[] = "Running... press any key to stop.";
Xstatic char qprompt[]  =
X"q to quit, RETURN/h/d/w to step by StpSz/hr/day/wk, or any other to freerun";
X
X/* used to locate, record and then erase last plotted chars */
Xtypedef struct {
X    double l_fr, l_fc;    /* 2d coords as 0..1 (upper left corner is (0,0)) */
X    int     l_r, l_c;    /* screen 2d coords (upper left corner is [1,1]) */
X    char l_tag;        /* char to use to print on screen */
X} LastDraw;
X
Xstatic int trails;    /* !0 if want to leave trails */
X
Xwatch (np, tminc, wbodies)
XNow *np;    /* time now and on each step */
Xdouble tminc;    /* hrs to increment time by each step */
Xint wbodies;    /* each bit is !=0 if want that body */
X{
X    static char *flds[4] = {
X        "Sky dome", "Alt/az sky", "Solar system"
X    };
X    static int fn;    /* begin with 0, then remember for next time */
X    int didone = 0;
X
X    while (1) {
X        int nf;
X        flds[3] = trails ? "Leave trails" : "No trails";
X        if ((nf = popup (flds, fn, 4)) < 0)
X        break;
X        fn = nf;
X        switch (nf) {
X        case 0: watch_sky (DOMESKY, np, tminc, wbodies); didone = 1; break;
X        case 1: watch_sky (ALTAZSKY, np, tminc, wbodies); didone = 1; break;
X        case 2: watch_solarsystem (np, tminc, wbodies); didone = 1; break;
X        case 3: trails ^= 1; break;
X        }
X    }
X
X    if (didone)
X        redraw_screen(2);
X}
X
X/* full alt/az or dome sky view (like the popular astro mags).
X * alt/az: north is at left and right of screen, south at center.
X *   0 elevation is at bottom of screen, zenith at the top.
X * dome: east is left, north is up.
X */
Xstatic
Xwatch_sky (style, np, tminc, wbodies)
Xint style;    /* DOMESKY or ALTAZSKY */
XNow *np;    /* time now and on each step */
Xdouble tminc;    /* hrs to increment time by each step */
Xint wbodies;    /* each bit is !=0 if want */
X{
X    static char east[] = "East";
X    static char west[] = "West";
X    static char north[] = "North";
X    static char south[] = "South";
X    double tminc0 = tminc;    /* remember the original */
X    /* two draw buffers so we can leave old up while calc new then
X     * erase and draw in one quick operation. always calc new in newp
X     * buffer and erase previous from lastp. buffers alternate roles.
X     */
X    LastDraw ld0[NOBJ], ld1[NOBJ], *lp, *lastp = ld0, *newp = ld1;
X    int nlast = 0, nnew;
X    int once = 1;
X    double lmjd, tmp;
X    Sky s;
X    int p;
X
X    /* clear screen and put up the permanent labels */
X    c_erase();
X    if (style == DOMESKY) {
X        double a;
X        for (a = 0.0; a < 2*PI; a += PI/8)
X        f_char (fr2r(.5-sin(a)/2.),
X            fc2c(.5+cos(a)/2./ASPECT) + ((a>PI/2 && a<3*PI/2) ? -1 : 1),
X            '*');
X        f_string (fr2r(.5), fc2c(.5-.5/ASPECT)-7, "East");
X        f_string (fr2r(1.), fc2c(.5)-2, south);
X        f_string (fr2r(.5), fc2c(.5+.5/ASPECT)+4, "West");
X        f_string (2, NC/2-2, north);
X    } else {
X        f_string (NR, 1, north);
X        f_string (NR, NC/4, east);
X        f_string (NR, NC/2, south);
X        f_string (NR, 3*NC/4, west);
X        f_string (NR, NC-5, north);   /* -1 more to avoid scrolling */
X        f_string (2, NC/2-3, "Zenith");
X    }
X    f_string (2, 1, tznm);
X    f_string (3, 1, "LST");
X
X    while (1) {
X        if (once)
X        print_updating();
X
X        /* calculate desired stuff into newp[] */
X        nnew = 0;
X        for (p = nxtbody(-1); p != -1; p = nxtbody(p))
X        if (wbodies & (1<<p)) {
X            (void) body_cir (p, SKYACC, np, &s);
X            if (s.s_alt > 0.0) {
X            LastDraw *lnp = newp + nnew;
X            if (style == DOMESKY) {
X                tmp = 0.5 - s.s_alt/PI;
X                lnp->l_fr = 0.5 - tmp*cos(s.s_az);
X                lnp->l_fc = 0.5 - tmp*sin(s.s_az)/ASPECT;
X            } else {
X                lnp->l_fr = 1.0 - s.s_alt/(PI/2);
X                lnp->l_fc = s.s_az/(2*PI);
X            }
X            lnp->l_tag = body_tags[p];
X            nnew++;
X            }
X        }
X        set_screencoords (newp, nnew);
X
X        /* unless we want trails,
X         * erase any previous tags (in same order as written) from lastp[].
X         */
X        if (!trails)
X        for (lp = lastp; --nlast >= 0; lp++)
X            f_char (lp->l_r, lp->l_c, ' ');
X
X        /* print LOCAL time and date we will be using */
X        lmjd = mjd - tz/24.0;
X        f_time (2, 5, mjd_hr(lmjd));
X        f_date (2, 14, mjd_day(lmjd));
X        now_lst (np, &tmp);
X        f_time (3, 5, tmp);
X
X        /* now draw new stuff from newp[] and park the cursor */
X        for (lp = newp; lp < newp + nnew; lp++)
X        f_char (lp->l_r, lp->l_c, lp->l_tag);
X        c_pos (PARK_ROW, PARK_COL);
X        fflush (stdout);
X
X        /* swap new and last roles and save new count */
X        if (newp == ld0)
X        newp = ld1, lastp = ld0;
X        else
X        newp = ld0, lastp = ld1;
X        nlast = nnew;
X
X        if (!once)
X        slp_sync();
X
X        if (once || (chk_char()==0 && read_char()!=0)) {
X        if (readwcmd (tminc0, &tminc, &once) < 0)
X            break;
X        }
X
X        /* advance time */
X        inc_mjd (np, tminc);
X    }
X}
X
X/* solar system view, "down from the top", first point of aries to the right.
X * always include earth.
X */
Xstatic
Xwatch_solarsystem (np, tminc, wbodies)
XNow *np;    /* time now and on each step */
Xdouble tminc;    /* hrs to increment time by each step */
Xint wbodies;
X{
X    /* max au of each planet from sun; in astro.h #defines order */
X    static double auscale[] = {.38, .75, 1.7, 5.2, 11., 20., 31., 50.};
X    double tminc0 = tminc;    /* remember the original */
X    /* two draw buffers so we can leave old up while calc new then
X     * erase and draw in one quick operation. always calc new in newp
X     * buffer and erase previous from lastp. buffers alternate roles.
X     */
X    LastDraw ld0[2*NOBJ], ld1[2*NOBJ], *lp, *lastp = ld0, *newp = ld1;
X    int nlast = 0, nnew;
X    int once = 1;
X    double lmjd;
X    double scale;
X    Sky s;
X    int p;
X
X    /* set screen scale: largest au we will have to plot.
X     * never make it less than 1 au (with fudge) since we always show earth.
X     */
X    scale = 1.1;
X    for (p = MARS; p <= PLUTO; p++)
X        if ((wbodies & (1<<p)) && auscale[p] > scale)
X        scale = auscale[p];
X
X    /* clear screen and put up the permanent labels */
X    c_erase();
X    f_string (2, 1, tznm);
X
X    while (1) {
X        if (once)
X        print_updating();
X
X        /* calculate desired stuff into newp[].
X         * fake a sun at center and add earth first.
X         * (we get earth's loc when ask for sun)
X         */
X        nnew = 0;
X        set_ss (newp+nnew, 0.0, 0.0, 0.0, 'S');
X        nnew += 2;
X        (void) body_cir (SUN, SSACC, np, &s);
X        set_ss (newp+nnew, s.s_edist/scale, s.s_hlong, 0.0, 'E');
X        nnew += 2;
X        for (p = MERCURY; p <= PLUTO; p++)
X        if (p != MOON && (wbodies & (1<<p))) {
X            (void) body_cir (p, SSACC, np, &s);
X            set_ss (newp+nnew, s.s_sdist/scale, s.s_hlong, s.s_hlat,
X                                body_tags[p]);
X            nnew += 2;
X        }
X        for (p = OBJX; p != -1; p = (p == OBJX) ? OBJY : -1)
X        if (wbodies & (1<<p)) {
X            (void) body_cir (p, SSACC, np, &s);
X            if (s.s_hlong != NOHELIO && s.s_sdist <= scale) {
X            set_ss (newp+nnew, s.s_sdist/scale, s.s_hlong, s.s_hlat,
X                                body_tags[p]);
X            nnew += 2;
X            }
X        }
X
X        set_screencoords (newp, nnew);
X
X        /* unless we want trails,
X         * erase any previous tags (in same order as written) from lastp[].
X         */
X        if (!trails)
X        for (lp = lastp; --nlast >= 0; lp++)
X            safe_f_char (lp->l_r, lp->l_c, ' ');
X
X        /* print LOCAL time and date we will be using */
X        lmjd = mjd - tz/24.0;
X        f_time (2, 5, mjd_hr(lmjd));
X        f_date (2, 14, mjd_day(lmjd));
X
X        /* now draw new stuff from newp[] and park the cursor */
X        for (lp = newp; lp < newp + nnew; lp++)
X        safe_f_char (lp->l_r, lp->l_c, lp->l_tag);
X        c_pos (PARK_ROW, PARK_COL);
X        fflush (stdout);
X
X        /* swap new and last roles and save new count */
X        if (newp == ld0)
X        newp = ld1, lastp = ld0;
X        else
X        newp = ld0, lastp = ld1;
X        nlast = nnew;
X
X        if (!once)
X        slp_sync();
X
X        if (once || (chk_char()==0 && read_char()!=0)) {
X        if (readwcmd (tminc0, &tminc, &once) < 0)
X            break;
X        }
X
X        /* advance time */
X        inc_mjd (np, tminc);
X    }
X}
X
X/* fill in two LastDraw solar system entries,
X * one for the x/y display, one for the z.
X */
Xstatic
Xset_ss (lp, dist, lg, lt, tag)
XLastDraw *lp;
Xdouble dist, lg, lt;    /* scaled heliocentric distance, longitude and lat */
Xchar tag;
X{
X    lp->l_fr = 0.5 - dist*sin(lg)*0.5;
X    lp->l_fc = 0.5 + dist*cos(lg)*0.5/ASPECT;
X    lp->l_tag = tag;
X    lp++;
X    /* row is to show course helio altitude but since we resolve collisions
X     * by adjusting columns we can get more detail by smaller variations
X     * within one column.
X     */
X    lp->l_fr = 0.5 - dist*sin(lt)*0.5;
X    lp->l_fc = c2fc(SSZCOL) + (1 - lp->l_fr)/NC;
X    lp->l_tag = tag;
X}
X
X/* given a list of LastDraw structs with their l_{fr,fc} filled in,
X * fill in their l_{r,c}.
X * TODO: better collision avoidance.
X */
Xstatic
Xset_screencoords (lp, np)
XLastDraw lp[];
Xint np;
X{
X    LastDraw *lpi;    /* the current basis for comparison */
X    LastDraw *lpj;    /* the sweep over other existing cells */
X    int i;        /* index of the current basis cell, lpi */
X    int j;        /* index of sweep cell, lpj */
X    int n;        /* total cells placed so far (ie, # to check) */
X
X    /* idea is to place each new item onto the screen.
X     * after each placement, look for collisions.
X     * if find a colliding pair, move the one with the greater l_fc to
X     * the right one cell, then rescan for more collisions.
X     * this will yield a result that is sorted by columns by l_fc.
X     * TODO: don't just move to the right, try up too for true 2d adjusts.
X     */
X    for (n = 0; n < np; n++) {
X        lpi = lp + n;
X        i = n;
X        lpi->l_r = fr2r(lpi->l_fr);
X        lpi->l_c = fc2c(lpi->l_fc);
X      chk:
X        for (j = 0; j < n; j++) {
X        lpj = lp + j;
X        if (i!=j && lpi->l_r == lpj->l_r && lpi->l_c == lpj->l_c) {
X            if (lpj->l_fc > lpi->l_fc) {
X            /* move lpj and use it as basis for checks now */
X            lpi = lpj;
X            i = j;
X            }
X            if (++lpi->l_c > NC)
X            lpi->l_c = 1;
X            goto chk;
X        }
X        }
X    }
X}
X
X/* since the solar system scaling is only approximate, and doesn't include
X * object x/y at all, characters might get mapped off screen. this funtion
X * guards against drawing chars off screen. it also moves a char being drawn
X * on the lower right corner of the screem left one to avoid scrolling.
X */
Xstatic
Xsafe_f_char (r, c, tag)
Xint r, c;
Xchar tag;
X{
X    if (r >= 1 && r <= NR && c >= 1 && c <= NC) {
X        if (r == NR && c == NC)
X        c -= 1;
X        f_char (r, c, tag);
X    }
X}
X
X/* see what the op wants to do now and update prompt/times accordingly.
X * return -1 if we are finished, else 0.
X */
Xstatic int
Xreadwcmd (tminc0, tminc, once)
Xdouble tminc0;
Xdouble *tminc;
Xint *once;
X{
X    f_prompt (qprompt);
X
X    switch (read_char()) {
X    case END:         /* back to table */
X        return (-1);
X    case '\r': case ' ':    /* one StpSz step */
X        *tminc = tminc0;
X        *once = 1;
X        break;
X    case 'h':        /* one 1-hour step */
X        *tminc = 1.0;
X        *once = 1;
X        break;
X    case 'd':        /* one 24-hr step */
X        *tminc = 24.0;
X        *once = 1;
X        break;
X    case 'w':        /* 7 day step */
X        *tminc = 7*24.0;
X        *once = 1;
X        break;
X    default:        /* free-run */
X        *once = 0;
X        f_prompt (frprompt);
X    }
X    return (0);
X}
END_OF_FILE
  if test 12217 -ne `wc -c <'watch.c'`; then
    echo shar: \"'watch.c'\" unpacked with wrong size!
  fi
  # end of 'watch.c'
fi
echo shar: End of archive 2 \(of 9\).
cp /dev/null ark2isdone
MISSING=""
for I in 1 2 3 4 5 6 7 8 9 ; do
    if test ! -f ark${I}isdone ; then
    MISSING="${MISSING} ${I}"
    fi
done
if test "${MISSING}" = "" ; then
    echo You have unpacked all 9 archives.
    rm -f ark[1-9]isdone ark[1-9][0-9]isdone
else
    echo You still must unpack the following archives:
    echo "        " ${MISSING}
fi
exit 0
exit 0 # Just in case...