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1992-04-17
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Ephem V4.28 - February 24, 1992
Copyright (c) 1990,1991,1992 by Elwood Charles Downey
Table of Contents
1. Introduction ................................................... 3
1.1. References and Acknowledgements .............................. 3
2. Running Ephem .................................................. 4
2.1. Command Line Format .......................................... 4
2.2. Program Operation ............................................ 4
3. Screen Fields .................................................. 6
3.1. Top Screen Fields ............................................ 6
3.2. The "OCX" column ............................................. 7
3.3. Data format columns .......................................... 8
3.4. RiseSet format columns ....................................... 8
3.5. Separation format fields ..................................... 9
3.6. Jupiter Aux .................................................. 9
4. Date and Time Formats .......................................... 9
5. Configuration File ............................................. 10
5.1. Configuration File fields .................................... 10
5.2. Example ephem.cfg ............................................ 12
6. Menu options ................................................... 12
6.1. Adaptive vs. Standard hzn .................................... 12
6.2. Geocentric vs. Topocentric ................................... 13
7. User Defined Objects: X and Y .................................. 13
7.1. Controlling Object-X or Y Operation .......................... 13
7.1.1. Fixed ...................................................... 14
7.1.2. Elliptical ................................................. 14
7.1.3. Hyperbolic ................................................. 14
7.1.4. Parabolic .................................................. 15
7.1.5. Lookup ..................................................... 15
7.1.6. On or Off .................................................. 15
7.2. Magnitude models ............................................. 16
7.2.1. g/k model .................................................. 16
7.2.2. H/G model .................................................. 16
7.3. Database File ................................................ 17
8. Plotting ....................................................... 17
8.1. Defining plot fields ......................................... 18
8.2. Displaying a plot file ....................................... 18
8.3. Cartesian or Polar coords .................................... 18
8.4. Begin Plotting ............................................... 18
8.5. Stopping Plotting ............................................ 19
9. Listing ........................................................ 19
10. Watching ...................................................... 19
10.1. Trails ...................................................... 19
10.2. Sky dome .................................................... 19
10.3. Alt/az sky .................................................. 19
10.4. Solar System ................................................ 20
11. Searching ..................................................... 20
11.1. Find extreme ................................................ 20
11.2. Find 0 ...................................................... 21
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11.3. Binary ...................................................... 21
11.4. Define a New function ....................................... 21
11.4.1. Intrinsic functions ....................................... 21
11.4.2. Field Specifiers .......................................... 22
11.4.3. Constants ................................................. 22
11.4.4. Operators ................................................. 22
11.5. Specifying Search Accuracy .................................. 23
11.6. Stop ........................................................ 23
11.7. Example Searches ............................................ 23
11.8. Another Example ............................................. 24
11.9. Caution ..................................................... 24
12. Implementation Notes .......................................... 24
12.1. Program limits .............................................. 25
13. DOS Installation Procedure .................................... 26
13.1. Setting TZ .................................................. 26
14. Known Bugs and Wish List ...................................... 27
15. Sample Screens ................................................ 28
- 3 -
1. Introduction
Ephem is a program that displays ephemerides for all the planets plus any
two additional objects. The additional objects may be fixed or specified
via heliocentric elliptical, hyperbolic or parabolic orbital elements to
accommodate solar system objects such as asteroids or comets.
Information displayed about each object includes RA and Dec precessed to
any epoch, local azimuth and altitude, heliocentric coordinates, distance
from sun and earth, solar elongation, angular size, visual magnitude,
illumination percentage, local rise, transit and set times, length of time
up, constellation, and angular separations between all combinations of
objects. A special detail of Jupiter's moons and central meridian
longitude is also available.
Observing circumstance information includes UTC and local date and time,
local sidereal time, times of astronomical twilight, length of day and
night, local temperature, pressure and height above sea level for the
refraction model and a monthly calendar.
RA/Dec calculations are geocentric and include the effects of light travel
time, nutation, aberration and precession. Alt/az and rise/set/transit
and, optionally, angular separation calculations are topocentric and
include the additional effects of parallax and refraction.
Plot and listing files of selected field values may be generated as the
program runs. The plot files are full precision floating point values in
ASCII intended for export to other plotting programs. The listing files
are tables formatted for more general human reading. Ephem includes
simple quick-look facilities to view these files.
One may watch the sky or the solar system with a simple character-oriented
screen display.
Ephem may be asked to search for interesting conditions automatically,
using several algorithms. Most fields displayed on the screen may be used
as terms in an arbitrary arithmetic expression that can be solved for
local zero or extrema, or the time of state change of any boolean
expression can be found.
The program is some 11,000 lines of C. It uses only a very simple set of
io routines and should be easily ported to any 24x80 ASCII display. To
date, it has been ported to several flavors of Unix, VMS, MS-DOS and,
simplistically, the Macintosh using Think-C.
1.1. References and Acknowledgements
The planetary polynomials and correction algorithms are taken, with
permission, from "Astronomy With Your Personal Computer", by Peter
Duffett-Smith, Cambridge University Press, (c) 1985.
The constellation determination algorithm is from a paper by Nancy G.
Roman, "Identification of a constellation from a position", Publications
of the Astronomical Society of the Pacific, Vol. 99, pages 695-699, July
- 4 -
1987.
The precession routine is from 1989 Astronomical Almanac.
Jupiter's moons are based on information in "Astronomical Formulae for
Calculators" by Jean Meeus. Richmond, Va., U.S.A., Willmann-Bell, (c)1982.
This reference is suitable for identification purposes but is not accurate
enough for precise occultation work.
I would like to thank Craig Counterman for his very competent assistance,
Joseph Fedock for his faithful testing and encouragement, Karsten Spang,
Richard Dyson, Doug McDonald and Peter Newton for their contributions in
porting ephem to various systems, and the many others who have made
helpful suggestions along the way. Finally, I would like to thank all of
you who actually use ephem; it is most gratifying to make a program from
which others derive value.
2. Running Ephem
2.1. Command Line Format
To run ephem, just type "ephem". You may also specify an alternate
configuration file, an alternate database file, and specify initial values
for several screen fields. The command line syntax can be summarized as
follows:
ephem [-c <config_file>] [-d <database_file>] [field=value ...]
The default configuration file is named ephem.cfg in the current
directory. Ephem also looks for one named by the EPHEMCFG environment
variable, if it is set. You may specify an arbitrary name with the -c
option.
The default database file is named ephem.db in the current directory.
Ephem also looks for one named by the EPHEMDB environment variable, if it
is set. You may specify an arbitrary name with the -d option.
The exact format of these files is described below.
Any additional command line arguments are treated exactly as if they too
came from the configuration file.
2.2. Program Operation
When ephem starts, it first displays a disclaimer banner. Then, after any
key is pressed, it reads the configuration file and processes the command
line arguments to set the initial values of several fields, accessing the
database file if OBJX or OBJY is set, It then draws all fields on the
screen with their initial values. The program then loops advancing time
each step, by some amount you may control, and updating all fields each
loop.
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There are three fields that control this looping behavior. NStep controls
the number of steps, StpSz the amount of time to add each step, and Pause
is the amount of real seconds to pause between steps. Ephem does not
pause between steps when plotting or searching is on. When the number of
steps, NStep, goes to 0 or any key is pressed, the looping stops and you
enter a command mode.
Command mode allows you to modify most of the fields. The idea is that
you move to each field on the screen you wish to change and change it.
When you have changed everything you want to, type "q" to resume screen
updates.
To change a field:
1) move the cursor to the field (see below);
2) type RETURN;
3) type in the new value along the command line at the top according
to the format indicated in the prompt. To accept the new value
type RETURN, or to leave it unchanged after all type "q".
A few fields don't require you to type anything; just typing RETURN does
all the work. If you can't move to it, you can't change it.
The arrow keys on most systems move the cursor around. If these do not
function or function incorrectly, the h/j/k/l keys also move the cursor
left/down/up/right, respectively. Motions off any edge of the screen will
wrap around.
Several "hot-keys" move the cursor immediately to frequently used fields.
You may move the cursor immediately to a planet row by typing one of the
characters SMevmJsunpxy. "x" and "y" are for the user-defined objects X
and y on the bottom rows. Also, the characters c, d, o, w, L and z move
you to the Menu, UT Date, Epoch, Watch, Listing and StpSz fields
immediately.
When you have changed a field that would invalidate any of the other
fields the message NEW CIRCUMSTANCES appears in the top center of the
screen. This will remain until you type "q" to allow at least one screen
update loop to occur. If you change any field that causes new
circumstances, the StpSz value is not added to the first loop. Note also
that after a series of loops, NStep is automatically reset to 1 so "q"
will do exactly one loop and return you to command mode.
On some systems, you may temporarily escape from ephem while in command
mode to run your operating system's command interpretor. This is done by
typing an exclamation point (!) followed by your command. When the
command completes, you will return back to ephem where you left off.
To quit the program, type control-d from command mode. For a little more
help, type ?. The entire screen may be erased and redrawn with control-l.
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3. Screen Fields
The screen is divided into two halves, top and bottom. The top fields are
always present. They define the general observing circumstances and
control features.
The bottom half has several different forms. In three of the possible
forms the planets and two additional objects are displayed in a table.
There is one object per row, and several columns. The three forms of this
portion selected by picking the Menu selection.
The fourth form is a display of the planetocentric coordinates of the
Galilean moons of Jupiter, including a simple graphical display of their
locations as seen from Earth, and the central meridian longitude, in two
of the adopted rotational systems.
Some things may be turned off to reduce compute times. Calculations for
each planet may be turned on and off by selecting the planet name field.
Calculations for Dawn/Dusk/NiteLn may be turned off by selecting any of
these fields. Planet positions are only updated as often as necessary to
match the display precision of the screen unless plotting or searching is
on. In these cases full precision is desired at all times and so
positions are always fully recalculated at each iteration.
Follows is a list and description of each of the fields in each section.
Following each name a parenthetical "p" indicates the field may be
selected for plotting (see later). All fields may be selected for
changing.
3.1. Top Screen Fields
LTZ the local timezone name. The name field may be changed to
any three-character mnemonic.
LT(p)
LD(p) The local time and date are not labeled as such but are to
the right of the local timezone name. They are individually
selectable. Time and date fields may be changed as
described in a later section. Set to "n" to set to "now"
from computer clock.
UT(p)
UD(p) The universally coordinated time and date are not labeled as
such but are to the right of the UTC label. They are
individually selectable. Time and date fields may be
changed as described in a later section. Set to "n" to set
to "now" from computer clock.
JulianDat(p) the current Julian date, to about 1-second accuracy.
Listing controls listing; see complete discussion below.
Watch selects the sky dome, altitude/azimuth sky or solar system
displays; see complete discussion below.
Search controls the automatic search feature of ephem. See the
complete discussion below.
Plot controls plotting; see complete discussion below.
Menu controls which menu is in the bottom half of the screen.
- 7 -
See their complete discussion below.
LST(p) the current local sidereal time. set to "n" to set from
computer clock.
Dawn(p) local time when the sun center is 18 degrees below the
horizon before sunrise today.
Dusk(p) local time when the sun center is 18 degrees below the
horizon after sunset today.
NiteLn(p) length of astronomical night, ie, Dawn - Dusk. If this line
is shown as "-----", it means the sun is either always below
or always above approximately -18 degrees altitude on this
particular day. This and the Dawn and Dusk lines are blank
when their computation has been turned off.
NStep The number of times the display with be updated (time
advanced by StpSz each step) before entering command mode.
StpSz the amount of time UTC (and its derivatives) is incremented
each loop. set this to "r" to use real-time based on the
computer clock. you may also set it in terms of days by
appending a "d" after the number when you set it.
Lat(p) location latitude, positive degrees north of equator.
Long(p) location longitude, positive degrees west of Greenwich
meridian. set to "N" to set from computer clock.
Elev(p) local elevation of the ground above sea level, in feet. (see
implementation notes).
Temp(p) local surface air temperature, in degrees F.
AtmPr(p) local surface air pressure, in inches of mercury.
TZ(p) hours local time is behind utc, ie, positive west or
negative east of Greenwich.
Epoch the epoch, to the nearest 0.1 years, to which the ra/dec
fields are precessed. This says (OfDate) when coordinates
are not precessed, ie, are in the epoch of date. Set to "e"
to set to epoch of date.
Pause number of seconds to pause between screen updates. This is
used mainly to set up for free-running unattended operation.
This pause also applies to free-running "watch" screen
updates. Pausing is not done when plotting or searching is
on. If pausing is used with StpSz set to RT CLOCK and the
time was set with Now then ephem attempts to synchronize the
time to an integral multiple of pause seconds after the
minute, for aesthetic reasons.
Also in the upper right of the screen is a calendar for the current local
month. Dates of local new and full moons are marked NM and FM,
respectively.
3.2. The "OCX" column
The left column of the bottom screen, when displaying planetary
information, is labeled "OCX". This is short for "Object-Constellation-
eXtra". It is actually one, two or three adjacent one-column pickable
fields. Select the first column of the name to toggle the display and
calculations on and off. Select the second column of the name to show the
constellation in which the object currently resides. If available, the
third column of a planet name can be picked to display additional current
- 8 -
information relating to the planet. At this time, this feature is only
available for Jupiter.
3.3. Data format columns
R.A.(p) apparent geocentric right ascension of object, precessed to
given epoch, in hours, minutes and decimal minutes.
Dec(p) apparent geocentric declination of object, precessed to
given epoch, in degrees and minutes.
Az(p) degrees eastward of true north for object.
Alt(p) degrees up from a horizontal plane Elev feet above sea
level.
H Long(p) true heliocentric longitude, in degrees. Earth's is
displayed on the sun's line. For the moon this is the
geocentric longitude.
H Lat(p) true heliocentric latitude, in degrees. For the moon this
is the geocentric latitude.
Ea Dst(p) true distance from Earth center to object center, in AU,
except distance to the moon is in miles.
Sn Dst(p) true distance from sun center to object center, in AU.
Elong(p) spherical angular separation between sun and given object,
calculated from the their geocentric ecliptic coordinates.
Note this is not just the difference in ecliptic longitude.
The sign, however, is simply sign(obj's longitude - sun's
longitude), ie, degrees east. thus, a positive elongation
means the object rises after the sun. This field is not
generally useful in searching for conjunctions because of
the discontinuous sign change that occurs at conjunction.
Size(p) angular size of object, in arc seconds.
VMag(p) visual magnitude of object.
Phs(p) percent of visible surface in sunlight. Note the moon phase
is calculated simplistically as just abs(elongation)/180*100
which can be a few degrees off... this means that because of
how elongation is defined it doesn't say 0 during new moon
(or 100 during full) except during close eclipses (maybe
that's a "feature"?).
Also, some terminals scroll when a character is written to the lower right
character position. To avoid this, Object Y's phase is left shifted by one
column. This can look particularly ugly when the phase is 100% because the
"100" is right next to visual magnitude number.
If desired, the angle between Earth and Sun from the object, p, can be
computed from the illumination percentage, i, with the following relation:
cos (p) = i/50 - 1
3.4. RiseSet format columns
Rise Time
Rise Az The local time and azimuth when the upper limb of the object
rises today.
Transit Time
Transit Alt The local time and altitude when the object crosses the
meridian today, ie, when its azimuth is true south or, if no
precession, when the local sidereal time equals the object's
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right ascension.
Set Time
Set Az The local time and azimuth when the upper limb of the object
sets today.
Hours Up The number of hours the object is up on the local date.
Horizon displacement may be calculated in either of two ways; see the
horizon discussion in the Menu selection section.
Various oddball conditions are accounted for, including an object that is
up sometime during the day but that doesn't rise, transit or set as such
on that day, an object that is circumpolar or that is never up or one that
rises twice on the same day. These are marked as "Never rises", "Never
transits", "Never sets", "Circumpolar", "Never up" or appended with a plus
"+" sign, respectively.
3.5. Separation format fields
This format is a table of angular separations between each pair of
objects. These angles are based on the local altitude/azimuth, and so in
general differ somewhat from the elongations reported for the sun in the
Data menu.
Unfortunately, with the format "ddd:mm", there is not enough room for a
space between columns when the angle is at least 100 degrees. To avoid
this, ephem drop the minutes portion if the (rounded) angle is at least
100 degrees.
3.6. Jupiter Aux
This menu option is a table of X, Y and Z coordinates for each of the
moons of Jupiter known to Galileo Galilei, that is, its four brightest.
The coordinate system is such that the xy plane is the mean plane of the
moons orbits, with +x to the east, +y to the north, and +z towards earth.
The y coordinate is corrected for earth's angular displacement above or
below this plane.
The menu also displays the longitude of the central meridian of Jupiter.
Three rotational systems have been adopted for this purpose; we show the
two that are useful to visual work.
4. Date and Time Formats
Times are displayed and entered in h:m:s format. If you pick a time field
to change it any of the h, m, and s components that are not specified are
left unchanged from their current value. For example, 0:5:0 set hours to
0, minutes to 5, seconds to 0, whereas :5 sets minutes to 5 but leaves
hours and seconds unchanged. A negative time is indicated by a minus sign
(-) anywhere before the first digit.
Dates are displayed and entered in American month:day:year format. As
with time, components omitted when entering a new value retain the current
value. For example, if the current date is 10/20/1988 and you type 20/20
the new date will become 20/20/1988. Note you must type the full year
since the program is accurate over several centuries either side of 1900.
If you change the date, the time (ie, partial day) will not change.
Negative years indicate BC dates. For example, Jan 1, 1 BC is given as
1/1/-1. There is no year 0.
- 10 -
Two other ways to set the date are supported for compatibility with some
published comet ephemerides. You may enter the day portion as a real
number. When you set the day this way, the time will also change to
correspond to the fractional portion of the day.
You may also enter a date as a decimal year, as in 1990.12345. This is
also useful in interpreting plot files that include a date field, since
date fields are stored in plot files as decimal years. If no decimal
point is included, the number is assumed to be a year unless it is in the
range 1-12, in which case it will be taken to mean that you are just
changing the month of the current date. To actually specify the years 1 -
12, you must append a decimal point to distinguish them from months.
As a matter of typing convenience, the program accepts most any character
as the separator; you don't have to type a perfect ":" or "/".
5. Configuration File
The ephem.cfg configuration file allows you to set the initial values of
many of the screen fields. You can still change any field while the
program is running too; this file just sets the initial conditions. Note
that the order of entries in this file is important because they each take
effect immediately. You should put them in the same order you wish them
to be processed, just as though you were changing the fields interactively
within ephem.
The default name of the file is ephem.cfg. Ephem also looks for one named
by the EPHEMCFG environment variable (if defined) or you may specify any
name using the -c command line option.
The format of the file uses the form KEYWORD=VALUE, where the possible
KEYWORDS and the types of VALUES for each are described below. Any
KEYWORDS not in the file will take on some sort of default. The separator
need not be an actual equals sign; any char will do because the VALUE is
assumed to start one character after the KEYWORD, regardless.
All lines that do not begin with an alpha character (a through z, either
case) are ignored and may be used for comments.
Note: because of the way unspecified time and date components are left
unchanged (see section on Date and Time Formats) always specify the
complete time and date for all entries in the configuration file. For
example, to initialize the longitude to zero degrees, say 0:0:0, not just
0.
5.1. Configuration File fields
UD initial UTC date, such as 10/20/1988, or "NOW" to use the
computer clock.
UT initial UTC time, such as 12:0:0, or "NOW" to use the computer
clock.
TZONE hours the local time is behind utc, such as 5:0:0. you need not
set this if you use "NOW" for UT or UD.
TZNAME name of the local time zone, such as CDT. 3 chars max. you need
not set this if you use "NOW" for UT or UD.
LONG longitude, in degrees west of Greenwich, in the form d:m:s.
- 11 -
LAT latitude, in degrees north of the equator, in the form d:m:s.
HEIGHT height above sea level, in feet, such as 800
TEMP air temperature, in degrees F, such as 50
PRES air pressure, in inches of Mercury, such as 29
STPSZ the time increment between screen updates, such as "1" to give
one hour updates. this can be a specific amount or RTC to use
the system clock as a real-time source. You may also specify a
time in days, by appending a D (or d) after the number.
PROPTS this selects what you want included initially in the display.
since IBM-PC math is not very fast, you can reduce the time to
update the screen by only printing those fields of interest. the
VALUE is a collection of letters to turn on each item from the
following set:
T twilight (dawn-dusk)
S circumstances for the sun
M circumstances for the moon
e circumstances for mercury
v circumstances for venus
m circumstances for mars
j circumstances for jupiter
s circumstances for saturn
u circumstances for uranus
n circumstances for neptune
p circumstances for pluto
x circumstances for object X
y circumstances for object Y
For example, to just track the sun and saturn, say PROPTS=Ss
If the delimiter between PROPTS and the selection is a plus (+)
sign then the given planets are included IN ADDITION TO ones
already specified. Any other delimiter sets the selection to
exactly the set specified. This feature was added so that the
command line version of using PROPTS could add to the set of
planets giving in the configuration file.
NSTEP number of times program will loop before entering command mode.
see the discussion under Program Operation.
EPOCH this sets the desired ra/dec precession epoch. you can put any
date here or EOD to use the current instant ("Epoch of Date").
OBJX
OBJY These fields specify the optional objects "x" and "y" by naming
any item in the database file. The form is OBJX=xyz, where xyz
must be in the database file, case sensitive. You may define
one object of each type for each of OBJX and OBJY; the last one
defined will be the "current" one when ephem gets going.
PAUSE The number of seconds to pause between calculation steps. See
definition of the Pause field in the "Top Screen Fields"
section.
MENU establishes the initial bottom screen menu type. This should be
one of the keywords DATA, RISET, SEP or JUP. There is no way to
set horizon or center suboptions at this time.
- 12 -
5.2. Example ephem.cfg
This is the ephem.cfg file that was in effect when the sample screens (in
another section) were generated. You might run ephem with this
configuration file and compare with the samples as a check.
UT=0;0;0
UD=5/1/1990
TZNAME=CDT
TZONE=5
LONG=93:42:8
LAT=44:50:37
HEIGHT=800
TEMP=40
PRES=29.5
STPSZ=RTC
PROPTS=TSMevmjsunpxy
EPOCH=2000
NSTEP=1
OBJX=Austin
OBJY=Juno
As another common example, this ephem.cfg creates an essentially free-
running real-time screen based on the computer clock:
UT=Now
LONG=90:10:8
LAT=40:50:20
HEIGHT=800
TEMP=50
PRES=29
STPSZ=RTC
PROPTS=TSMevmjsunp
NSTEP=9999999
EPOCH=Eod
PAUSE=30
6. Menu options
When you select "Menu" you can change among the three styles of bottom
screens. There are also two options that can be set from the Menu quick-
choice menu. These options toggle when picked and retain their values so
they need only be changed when desired.
6.1. Adaptive vs. Standard hzn
This selects the horizon refraction displacement algorithm used by the
Rise/Set menu. "Adaptive" uses the local atmospheric conditions known to
ephem and matches the Planet Info times nicely. "Standard" uses the
"accepted nominal" horizon refraction value of 32 arc minutes and usually
agrees, to a minute or so, with published tables.
- 13 -
6.2. Geocentric vs. Topocentric
This selects the vantage point for the Separation menu. "Geocentric"
ignores local conditions and gives the separation as seen from Earth
center. "Topocentric" uses the local conditions known to ephem. They are
particularly critical for lunar occultations, but the effect can be
significant for the planets.
Note that searching over a period that will include the rise or set times
of either object is generally better performed from the geocentric
viewpoint. The refraction effect of the topocentric viewpoint causes many
arcminutes of rapid whiplash displacement as the objects rise and set that
overlays the smooth celestial motion of the objects. This rapid position
variation can confuse the solver algorithms that expect fairly smooth
functions.
7. User Defined Objects: X and Y
You may specify one or two extra objects for ephem to use. The objects may
be defined in four different ways: fixed celestial sphere coordinates, or
heliocentric elliptical, hyperbolic or parabolic orbital elements.
Elliptical elements are typically useful for periodic comets or asteroids,
and hyperbolic and parabolic elements are for nonrecurring solar system
interlopers such as aperiodic comets.
The parameters for each type of object are stored separately, so you may
switch between types of objects without losing parameters.
7.1. Controlling Object-X or Y Operation
To control the type and the corresponding details for object X or Y,
select the corresponding row near the bottom. (Remember that typing the
character "x" or "y" is a shorthand way to move to the bottom rows.) It
will bring up a quick-choice menu as follows:
Select: Fixed, Elliptical, Hyperbolic, Parabolic, Lookup, On
When you first enter the quick-choice menu the cursor will start out
positioned at the field for the current type of object. The first four
selections allow you to enter or review the various parameters required to
define an object's position of the respective type, one parameter at a
time.
You set the current object type and begin to view its parameters by
positioning the cursor over the type and pressing RETURN. The prompt for
each item includes a short description, the units to use, and its current
setting is shown in parentheses. To leave the item unchanged and go to the
next item, type RETURN. If you do not wish to change or see any more
items about the object then type "q" and you will return immediately to
the object-X quick-choice menu.
You exit the quick-choice menu by typing "q" while over any field or
RETURN while over On or Off, as described in a later section.
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As with all dates throughout ephem, the dates for the epochs of perihelion
and reference epochs may be entered in month/day/year or decimal year
formats, and the day may be entered as a real number (see the section on
Date and Time Formats). All dates given for comet parameters are always
in UT.
7.1.1. Fixed
This selection will present a series of six prompts to define a fixed
object. The prompts are the name, RA, Dec, magnitude, the reference epoch
for the coordinates and the angular size in arc seconds.
7.1.2. Elliptical
This will begin a series of 13 prompts asking for a name and the
parameters that define a heliocentric elliptic orbit and the coefficients
for either of two magnitude models. These elements are the same ones
often listed in the Astronomical Almanac. The elements are, in order:
i = inclination, degrees
O = longitude of ascending node, degrees
o = argument of perihelion, degrees
a = mean distance (aka semi-major axis), AU
n = daily motion, degrees per day
e = eccentricity
M = mean anomaly (ie, degrees from perihelion)
E = epoch date (ie, time of M)
D = the equinox year (ie, time of i/O/o)
g/k or H/G = either of two magnitude models; see below
s = angular size at 1 AU, arc seconds
You might have other parameters available that can be converted into
these. The following relationships might be useful:
P = sqrt(a*a*a)
p = O + o
n = 360/days_per_year/P ~ 0.98563/P
T = E - M/n
q = a*(1-e)
where
P = the orbital period, years;
p = longitude of perihelion, degrees
T = epoch of perihelion (add multiples of P for desired range)
q = perihelion distance, AU
Note that if you know T you can then set E = T and M = 0.
7.1.3. Hyperbolic
This will begin a series of 11 prompts asking for a name and the
parameters that define a heliocentric hyperbolic orbit and the magnitude
model coefficients. These orbital parameters are, in order:
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T = epoch of perihelion
i = inclination, degrees
O = longitude of ascending node, degrees
o = argument of perihelion, degrees
e = eccentricity,
q = perihelion distance, AU
D = the equinox year (ie, time of i/O/o).
g/k = magnitude model
s = angular size at 1 AU, arc seconds
As with elliptical elements, other parameters might be available. The
relationships are generally the same, except for:
q = a*(e-1)
7.1.4. Parabolic
This will begin a series of 10 prompts asking for a name and the
parameters that define a heliocentric parabolic orbit and the magnitude
model coefficients. These orbital parameters are, in order:
T = epoch of perihelion
i = inclination, degrees
o = argument of perihelion, degrees
q = perihelion distance, AU
O = longitude of ascending node, degrees
D = the equinox year (ie, time of i/O/o).
g/k = magnitude model
s = angular size at 1 AU, arc seconds
7.1.5. Lookup
This option displays the name of each object in the database file. Move
around the list (using the usual hjkl or arrow keys) and type RETURN to
select an object. The cursor wraps around all edges. If there is more
than one page of entries, you may view the next or previous pages by
typing "n" or "p", respectively. Typing "q" will exit the lookup function
with no net effect.
If successful, the cursor will move to the type of the new object and it
becomes the current type.
7.1.6. On or Off
The last selection on the right toggles the calculations for the object On
and Off. It toggles when selected with RETURN and then immediately exits
the quick-choice menu back to the main menu. If calculations become On,
then they will be performed for the current type of object; if they become
Off the object-X or Y row of information will be erased.
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7.2. Magnitude models
Ephem supports two different magnitude models. One, denoted here as g/k,
is generally used for comets and is always used for hyperbolic and
parabolic objects and optionally for elliptical objects. The other,
denoted H/G, is generally used for asteroids in the Astronomical Almanac
and may be used with elliptical objects.
7.2.1. g/k model
This model requires two parameters to be specified. One, the absolute
magnitude, g, is the visual magnitude of the object if it were one AU from
both the sun and the earth. The other, the luminosity index, k,
characterizes the brightness change of the object as a function of its
distance from the sun. This is generally zero, or very small, for inactive
objects like asteroids. The model may be expressed as:
m = g + 5*log10(D) + 2.5*k*log10(r)
where:
m = resulting visual magnitude;
g = absolute visual magnitude;
D = comet-earth distance, in AU;
k = luminosity index; and
r = comet-sun distance.
Note that this model does not take into account the phase angle of
sunlight.
When using this model for elliptical objects, the first of the two
magnitude fields must be preceded by a letter "g" in both the ephem.db
database file and the corresponding quick-choice elliptical object
definition prompt; otherwise the default magnitude model for elliptical
objects is the H/G model.
7.2.2. H/G model
This model also requires two parameters. The first, H, is the magnitude of
the object when one AU from the sun and the earth. The other, G, attempts
to model the reflection characteristics of a passive surface, such as an
asteroid. The model may be expressed with the following code fragment:
beta = acos((rp*rp + rho*rho - rsn*rsn)/ (2*rp*rho));
psi_t = exp(log(tan(beta/2.0))*0.63);
Psi_1 = exp(-3.33*psi_t);
psi_t = exp(log(tan(beta/2.0))*1.22);
Psi_2 = exp(-1.87*psi_t);
m = H + 5.0*log10(rp*rho) - 2.5*log10((1-G)*Psi_1 + G*Psi_2);
where:
m = resulting visual magnitude
rp = distance from sun to object
rho = distance from earth to object
rsn = distance from sun to earth
Note that this model does not take into account the phase angle of
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sunlight.
This is the default magnitude model for elliptical objects but it can also
be explicitly indicated when the first of the two magnitude fields is
preceded by a letter "H" in both the ephem.db database file and the
corresponding quick-choice elliptical object definition prompt.
7.3. Database File
You may save a list of objects in a file to be used for setting OBJX and
OBJY. The default name of this file is ephem.db. You may also set it from
the command line with the -d option, or set it with the EPHEMDB
environment variable.
The file consists of one object per line. All lines that do not begin
with an alpha character are ignored and may be used for comments. Each
line contains several fields, each separated by a comma. The first field
is the name of the object. The second field is the type of the object,
that is, one of the strings "fixed", "elliptical", "hyperbolic" or
"parabolic"; actually, "f", "e", "h" and "p" are sufficient. The
remaining fields depend on the type of object. They are exactly the same
parameters, and in the same order, as ephem asks for when defining the
object from the menu. The size field is last and is optional for
compatibility with older versions.
8. Plotting
Each time a field is drawn on the screen during a full screen update cycle
(that as, during automatic looping or a manual "q" command character from
the main menu but not from a screen redraw from control-l or when an
individual planet is turned on or a single time field is changed) its
full-precision value may be written to a file. This implies you may not
plot a field from other than the current menu at the time plotting is on.
You can append several plot runs together, however, if necessary.
Each line in the file consists of a tag character followed by two or three
floating point variables, all separated by commas. If there are two
values, they should be interpreted to be x and y (or perhaps r and theta).
If there is a third, it is a z or trace value.
For efficiency on systems that can compute a screen full faster than they
can display it, screen updates are suppressed while plotting is on and
NStep is greater than 1. This can greatly reduce the time to generate a
long plot file. Fields are still logged for plotting; they just are not
drawn on the screen.
The Plot field controls plotting. Whether plotting is currently active is
indicated by "on" or "off" immediately to its right.
Picking "Plot" brings up a quick-choice menu, as follows:
Select: Select fields, Display a plot file, Cartesian coords, Begin plotting
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8.1. Defining plot fields
Select the "Select fields" option. You will be asked to move the cursor
to the field you want to use as the x coordinate (abscissa), then asked to
choose the y coordinate (ordinate), then asked to choose an optional z
trace variable and finally a tag character. (Of course, you may have in
mind fields that are more appropriately displayed in other than Cartesian
coordinates, in which case think of x, y and z as dimensions.) If you type
q for either x or y then no more fields will be defined. If you type q
for the z field there will be no z field. You can not label a plot line
with the letter "q" at this time.
This then repeats so you may choose up to ten of these sets for any given
plot run. Each set defines what will become a line on the final plot.
Note that you may select the "Search" field to indicate use of the current
search function; that function must be defined by the time plotting is
turned on.
If you turn plotting off and back on the fields selected for plotting are
reactivated the same as they were last time. You may change them if
desired, of course, but there is no need to redefine them if you do not
wish to change them.
8.2. Displaying a plot file
Select the "Display a plot file" option to generate a crude plot on the
screen of an existing plot file previously created by ephem. The entries
in the file will be drawn on the screen using their tag characters; the
plot remains on the screen until you type any character.
The plot may be made in polar or Cartesian coordinates, depending on the
setting of the plotting mode in the quick-choice (see next section).
8.3. Cartesian or Polar coords
This toggles the plotting mode coordinate system. The mode remains until
changed. Polar coordinates assume the first numeric field in the plot
file is the radius, and the second is the angle counterclockwise from
right, in degrees.
8.4. Begin Plotting
If plot field lines are defined then the third option, "Begin plotting"
will be available. You will be asked for the name of the file to use. If
it already exists you will be asked whether to overwrite it or append to
it. You will also be asked for a title line that will become the next
line of the file, automatically prefixed with a "*" to make it a comment
line. Once you have chosen a file, plotting is on and the top menu
plotting status field changes to "on". The default plot file name is
ephem.plt. The values are written to the plot file each time they are
updated on the screen until you select "Plot" again and select the "Stop"
option to turn plotting back off.
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8.5. Stopping Plotting
If plotting is on, then selecting the Plot field in the top section will
turn plotting off. You may pick Plot again and resume with the same fields
by selecting "Begin plotting" again.
Note that due to internal buffering the plot file will not be completely
written to disk until plotting is turned off.
9. Listing
This feature works very much like Plotting. However, the fields you select
define columns of a table generated as ephem runs. These columns are look
exactly like their corresponding fields on the ephem screen and so are far
more readable than plot files.
See the section on Plotting for an explanation of the quick-choice menu.
The general operation is very much the same.
10. Watching
You may generate a simple drawing on the screen of the local sky in two
forms or the solar system by selecting "Watch". It will bring up a
quick-choice menu as follows:
Select: Sky dome, Alt/az sky, Solar system, No trails
10.1. Trails
You may either erase after each iteration or leave the tags up, referred
to as "trails". Picking the right-most choice will toggle between "No
trails" and "Leave trails"; you should set it as desired before you select
the style of sky plot you wish. Ephem will remember your selection.
10.2. Sky dome
This draws the currently active planets within a circle that represents
the locally visible hemisphere. This is similar to the formats commonly
used in the popular astronomy magazines. East is left, south is down,
west is right and north is up.
10.3. Alt/az sky
This is a cylindrical projection showing the currently active planets as
they would appear in the sky looking southwards at the current time and
date. The coordinate system is such that 0 degrees azimuth (north)
through 360 degrees (north, once around) is mapped to the horizontal
screen dimension, and 0 degrees altitude (level) through 90 degrees (the
zenith) is mapped to the vertical dimension. Thus, the bottom row is the
horizon and all across the top is the zenith.
- 20 -
10.4. Solar System
This selection draws the currently active planets as they would appear
looking "down from the top" of the ecliptic, with the sun at the center
and zero hours right ascension towards the right. The scale is adjusted
to roughly fill the screen according to the outer-most active planet.
Note that the scaling does not take into account the distances of the user
defined objects so, if they don't appear, select a planet that is at least
as far out as they are. The screen transformation assumes a screen aspect
width/height ratio of 4/3. Down the left column of the screen is the
heliocentric altitude of the planet above or below the ecliptic, drawn to
the same scale as the circular display. Values so close as to land on the
same line are sorted left to right; the S and E symbols always denote
heliocentric altitude 0.
In each style of display, pressing RETURN advances the time by whatever
amount StpSz is set to. Pressing "h" advances the time by one hour, "d"
advances by one day, and "w" advances by one week (seven days). Pressing
"q" returns to the watch quick-choice menu from which you may select
another display style or return to the main tabular display by typing
another "q". Pressing any other key starts an automatic loop with each
step advancing by StpSz; pressing any key stops the looping.
As symbols are placed, collisions (overstrikes) are avoided by moving
characters in such a way as to maintain increasing sorted order towards
the right.
When you return to the main menu, the last watched time will be maintained
as the current time. The StpSz is not changed.
11. Searching
Ephem can search for arbitrary conditions to exist among most displayed
fields. You first enter a function, then select from among three forms of
equation solvers to iteratively solve for the next time when the function
meets the requirements of the solver. The solver selects the next time for
which it wants the function evaluated and sets StpSz so that the next
iteration will occur at that time. The solvers continue to iterate until
either they achieve their goal or NStep reaches 0.
You may set NStep to be quite large and let ephem search unattended or set
it to 1 and watch it converge one step at a time. You may also plot at the
same time as search to record the exact steps ephem took to converge.
(But recall that screen updates are suppressed if plotting is also on).
The "Search" selection in the top half of the screen controls all
searching. Picking it brings up a quick-choice menu as follows:
Select: Find extreme, Find 0, Binary, New function, Accuracy
11.1. Find extreme
This search algorithm searches for a local maximum or a minimum in the
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search function, whichever it finds first. It begins by evaluating the
search function at the current time then for two more times each separated
by StpSz. It then fits these three points to a parabola and solves it for
the time of its maximum (or minimum). StpSz is set so that the next
iteration will evaluate at this point. This parabolic fit solution keeps
repeating until StpSz changes by less than the desired accuracy or until
the curve becomes so flat that an extrema appears too broad to find.
11.2. Find 0
This search algorithm uses the secant method to solve for the time at
which the search function is zero. The function is evaluated at the
current time and then again StpSz later to establish a slope for which the
x-intercept is found as the next zero guess. This is used to set StpSz for
the next desired time value and the slope hunting process repeats until
StpSz changes by less than the desired accuracy.
11.3. Binary
This search algorithm must be used with a search function that yields a
boolean result, ie, a true or false value. The idea is that the function
is assumed to be one truth value when evaluated at the present time, and
the opposite truth value when it is evaluated StpSz later. The algorithm
will then do a binary search for the time when the truth value changes.
The binary algorithm does not begin until the state change is bounded in
time. Initially, as long as the truth value at StpSz is the same as the
previous value the algorithm will just keep moving in time by StpSz
looking for when the state changes. That is, a linear search is initiated
to bound the state change, then the binary search proceeds.
11.4. Define a New function
Select "New function" to display the current search function. If you type
"q" it will be left unchanged. If you type RETURN it will be erased. If
you type anything else it will be compiled and, if there are no errors, it
will become the new search function. Once a valid function has been
stored, it will remain unless changed. If a search function is selected
and there is as yet no valid search function defined, you will
automatically be asked to enter one as though you had selected "New
function."
A search function consists of intrinsic functions, field-specifiers,
constants and operators, and precedence may be overridden with
parentheses.
11.4.1. Intrinsic functions
In this release, the only intrinsic functions available are abs(), which
returns the absolute value of its argument, and sqrt(), which returns the
square root of its argument.
- 22 -
11.4.2. Field Specifiers
A field in the bottom half of the menu is generally specified in the form
of "object_name.column_name". The object_name is enough of the planet or
moon name to be unique. Use "x" or "y" for the user-specified object X or
Y. The column_name is from the following table, depending on which menu
is up. In all cases additional characters may be entered but are ignored.
Also, you may use x, y and z to specify those columns of the Galilean
moons menu.
Planet Data Menu Rise/Set Menu Separation Menu
------------------ -------------------- ---------------
al Alt hr Hrs Up, or j Jup
az Az hu Hrs Up ma Mars
d Dec raz Rise Az me Merc
ed Ea Dst rt Rise Time mo Moon
el Elong saz Set Az n Nep
hla Helio Lat st Set Time pl Pluto
hlo Helio Long ta Transit Alt sa Saturn
ph Phs tt Transit Time su Sun
ra R.A. u Uranus
sd Sn Dst ve Venus
si Size
vm VMag
A few fields do not use this "dot" notation. The following top-half
fields are indicated using these codes:
da Dawn
du Dusk
n NiteLn
Use "jI" and "jII" to indicate one of the two rotational systems of
Jupiter's central meridian longitude.
Remember, searching may only involve fields being calculated for display
at the time the solver is active. While you can syntactically include any
field in a search function it is useless to define a search that uses
fields from other than the menu that is selected at the time the search is
running.
11.4.3. Constants
Constants may be integers or floating point numbers. The latter may be
expressed in scientific notation if desired. Examples include 100, .9,
1.234, 1e10 and 1.2e-4. Any number may be preceded by - to make it
negative.
11.4.4. Operators
The collection of arithmetic, relational and boolean operators provided
mimics those of C language as listed in the following table, in decreasing
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order of precedence. Operators grouped together have the same precedence
and all have left-to-right associativity. Parentheses may be used as
desired.
Symbol Meaning Resulting type
------ -------------------- --------------
* multiply arithmetic
/ divide arithmetic
+ add arithmetic
- subtract arithmetic
> greater than boolean
>= greater than or equal boolean
< less than boolean
<= less than or equal boolean
== equality boolean
!= inequality boolean
&& logical and boolean
|| logical or boolean
11.5. Specifying Search Accuracy
Selecting "Accuracy" allows you to specify when the search will stop. The
search algorithms will stop when StpSz becomes equal to or less than this
value. The default is one minute. If ephem has not yet converged to the
specified accuracy but NStep has decremented to 1, the searching will stop
but the search status field will still indicate which search procedure is
in effect. To try more iterations you may increase NStep and resume
searching. If the accuracy was achieved, the search status field will
switch to "off" with the number of "unused" steps remaining in NStep and
the last step size in the StpSz fields.
11.6. Stop
If searching is on, this option will also appear on the quick-choice menu
and may be selected to turn off the search.
11.7. Example Searches
As an example, let's find when Pluto again becomes the furthest planet
from Sol. You may find when the difference in their sun distance is zero,
or you might use a binary search on the condition that Pluto's sun
distance is larger then Neptune's.
To try the former approach select Search, select "Find 0", specify the
search function to be:
pl.sd - nep.sd
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set StpSz to something large like 10d, NStep to allow several iterations
like 20, and then type "q" to start the search and watch ephem do the
hunt. Ephem will settle on about 21:02 1/10/1999 UT.
To try a binary search, you first need to have some idea of when the event
will occur so you can eliminate the initial linear search for the state
change. We can start at, say, 1/1/1999, set StpSz to 30d, select Binary
search, specify the search function to be:
pl.sd > nep.sd
and go. Once it brackets the state change note how StpSz keeps being cut
in half but can go in either direction (sign) as it divides each interval
in half. Ephem will converge on the same answer.
11.8. Another Example
To find the time of last quarter moon during December, 1989, use the "Find
0" search algorithm to solve "moon.el + 90". (At last quarter, the moon
is 90 degrees west of the sun, or -90 east in ephem's elongation display.)
Set the initial time to mid-month, 12/15/1989, StpSz to 1 day and NStep to
10. Ephem takes only a few iterations to settle on 23:57 12/19 UT.
11.9. Caution
Beware that most celestial phenomena are generally pseudo-periodic in
nature. In early search steps ephem can easily skip over a local maxima
and find a later one, which, while correct, may not be what was desired.
In general, the closer you can be when you start the search the better
ephem can refine it; it is not as good with very broad searches that can
go "wild". Set StpSz large enough to offer significant change in the
function value, but small enough not to skip too far.
For example, Saturn and Neptune had three close approaches during 1989.
If you did not know this then just asking ephem to find a minimum would
have produced different results depending on the starting conditions.
When starting a search for a certain class of event it is a good idea to
first use the plotting or watching facility of ephem to get a broad
picture of the general circumstances then use ephem's search facility to
refine a given region (or create and inspect a plot file and do your own
interpolation directly from it separately).
Similarly, ephem's searching techniques are not good for eclipses because
the moon and sun are close every month; the trick is sorting through the
frequent conjunctions for ones that are particularly close. One needs a
way of establishing an envelope fit to the local extrema of a cyclic
function in order to find a more global extreme.
12. Implementation Notes
Remember that everything is for the current local time and day. So, for
example, the calendar marks moon events in local time; commercial
calendars usually mark the UT date. Similarly, the rise/set times are for
the current local day.
- 25 -
The program uses a horizontal plane tangent to the earth as the horizon
for all altitude calculations, rise/set events, etc. This is not the same
as the angle up from the local horizon unless the observer is directly on
the ground due to earth's curvature. The effect can be found from:
sin(a)**2 = (h**2 + 2Rh) / (R+h)**2
where:
R = radius of earth
h = height above ground (same units as R)
a = increase in altitude
For example, the effect is more than two arc minutes at a height of 5
feet.
Visual magnitudes are not very accurate ... I haven't bothered to fix.
The accuracy of ephem can not be specifically stated since the Duffett-
Smith book does not warrant its planet position polynomials to any given
degree. I know for sure that better accuracy could be achieved if ephem
used TDT but I have not yet decided on a suitable algorithm. Allowing for
this manually, (see the Wish List section) comparisons with the
Astronomical Almanac are often within a few arcseconds.
The program uses double precision throughout. While this precision might
seem a little ridiculous, it is actually more efficient for most
traditional K&R C compilers and the search functions seem to be are far
more stable.
Searching and plotting always use full precision but if neither of these
are turned on pure display and watching only recompute a given planets new
location if the time has changed enough to effect the required display
precision, based on the planets mean apparent orbital motion.
The sun-moon distance is the solution for the third side of a planar
triangle whose two other sides are the earth-moon distance and earth-sun
distance separated by the angle of elongation.
Beware of computing with the user-defined objects before they are properly
defined.
If a floating point exception occurs ephem will stop further computations
on the current screen update and stop any automatic looping.
12.1. Program limits
The search function is limited to a maximum of 32 instructions (each
constant, field spec, and operation is one instruction), with no more than
a total of 16 constants and field specs. At run time, the function can not
require more than 16 stacked values (due to operator precedence or
explicit parenthetical expressions) to evaluate.
No more than 32 different fields can be tracked simultaneously for
plotting and/or searching.
- 26 -
No more than 10 lines may be plotted at once.
The maximum file name length is 14 characters.
13. DOS Installation Procedure
You must be running DOS V2.0 or later, though somewhere between V2.0 and
V3.21 the behavior of control-c to terminate the program was fixed. An
8087 floating point chip will be used if present.
The distribution floppy contains five files:
README describes last minute items and details of this release.
MAN.TXT is this manual, hopefully formatted and printable on most any
printer.
EPHEM.EXE is the executable program.
EPHEM.CFG is a sample configuration file.
EPHEM.DB is a sample database.
To run the program, make working copies of these files in a directory and
run "ephem" from that directory.
13.1. Setting TZ
Before running ephem, you should set a DOS environment variable, TZ. It
is is used to establish the timezone name and hours offset whenever the
"Now" shorthand is used from ephem, either from the configuration startup
file or whenever any time field is changed manually. Set it in the
following form:
set TZ=SSSnDDD
where
SSS is the 3-letter abbreviation for the local standard timezone;
n is a number between -23 to 24 indicating the number of hours that are
subtracted from GMT to obtain local standard time;
DDD is an optional 3-letter abbreviation for the local daylight savings
time zone name. Leave it off if you do not have savings time in your
area or it is not currently in effect. If the changeover dates differ
from the internal algorithm, just use SSS and n directly.
For example, in the midwestern United States with savings times set
TZ=CST6CDT
If for some reason your system does not change to savings time at the
right time, then omit the DDD parameter and just set the SSS and n to
exactly what you want.
You can put this in your AUTOEXEC.BAT file so it gets set each time you
boot DOS.
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14. Known Bugs and Wish List
incorporate Terrestrial Dynamical Time (known as Ephemeris Time prior to
1984). TDT is about 57 seconds ahead of UT1 in 1990.
it's too easy to turn on objx/y before it's defined and bomb out.
add explicit searching for eclipses and occultations.
in watch mode, RTC reverts back to being based off the time when watch was
first entered.
add a facility (or tool) to find g/k from a set of observed magnitudes.
add search criteria and a screen-based selection mechanism for database
objects.
add plot options to reverse x and/or y direction and add some tick marks.
continue pursuit of moon and other information for other planets.
add shorthands for some sidereal and synodic step sizes.
the built-in elements for pluto need to be updated. the elements for pluto
in the included ephem.db database sampler are more accurate.
plotting or listing rise/set that doesn't happen just reshows the last
entry.
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15. Sample Screens
Here are sample ephem screens. They are generated using the first sample
ephem.cfg file (listed in the section describing the configuration file).
There is one for each of the possible screen formats. The rise/set screen
was done using the Adaptive option. The separations screen was done using
the Topocentric option.
Move to another field, RETURN to change this field, ? for help, or q to run
CDT 19:00:00 4/30/1990 | LST 8:19:50 | Lat 44:50:37 | April 1990
UTC 0:00:00 5/01/1990 | | Long 93:42:08 | Su Mo Tu We Th Fr Sa
JulianDat 2448012.50000 | Dawn 4:10 | Elev 800 ft | 1 2 3 4 5 6 7
Watch | Dusk 22:15 | Temp 40 F | 8 FM 10 11 12 13 14
Listing off | NiteLn 5:55 | AtmPr 29.50 in | 15 16 17 18 19 20 21
Search off | | TZ 5:00:00 | 22 23 NM 25 26 27 28
Plot off | NStep 1 | Epoch 2000.0 | 29 30
Menu Planet Data | StpSz RT CLOCK | Pause 0 |
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OCX R.A. Dec Az Alt H Long H Lat Ea Dst Sn Dst Elong Size VMag Phs
Su 2:32.3 14:58 278:40 12:38 220:22 1.0075 1905 -27
Mo 8:09.9 21:11 186:06 65:53 119:55 1:04 234821 1.0071 79.5 1897 -12 44
Me 2:49.4 17:39 277:48 17:26 214:08 1:43 0.5764 0.4360 4.9 11.7 1.6 1
Ve 23:49.4 -2:25 296:53 -27:39 282:39 -1:30 0.9288 0.7276 -43.9 18.2 -4.8 64
Ma 22:39.8 -10:09 308:17 -44:14 297:56 -1:43 1.5438 1.4067 -62.9 6.1 0.3 89
Ju 6:30.9 23:23 235:13 59:04 106:16 0:08 5.6806 5.1941 56.6 34.6 -2.0 99
Sa 19:49.6 -20:53 17:24 -65:14 289:45 0:10 9.7077 10.017 -105.0 17.1 1.1 100
Ur 18:41.9 -23:24 51:18 -60:39 276:55 -0:18 18.864 19.401 -120.9 3.5 5.6 100
Ne 19:03.2 -21:46 40:51 -62:01 282:48 0:51 29.754 30.207 -115.8 2.1 7.9 100
Pl 15:14.8 -1:26 81:18 -10:37 226:18 15:28 28.693 29.658 -162.9 0.3 13.6 100
X 0:08.3 36:01 316:59 5:58 238:20 26:29 0.5622 0.6657 -38.4 0.0 1.5 33
Y 15:22.9 -2:40 80:43 -12:54 226:17 10:49 2.3635 3.3381 -162.5 0.0 10.1100
- 29 -
Move to another field, RETURN to change this field, ? for help, or q to run
CDT 19:00:00 4/30/1990 | LST 8:19:50 | Lat 44:50:37 | April 1990
UTC 0:00:00 5/01/1990 | | Long 93:42:08 | Su Mo Tu We Th Fr Sa
JulianDat 2448012.50000 | Dawn 4:10 | Elev 800 ft | 1 2 3 4 5 6 7
Watch | Dusk 22:15 | Temp 40 F | 8 FM 10 11 12 13 14
Listing off | NiteLn 5:55 | AtmPr 29.50 in | 15 16 17 18 19 20 21
Search off | | TZ 5:00:00 | 22 23 NM 25 26 27 28
Plot off | NStep 1 | Epoch 2000.0 | 29 30
Menu Rise/Set Info | StpSz RT CLOCK | Pause 0 |
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OCX Rise Time Rise Az Trans Time Trans Alt Set Time Set Az Hours Up
Su 6:05 67:48 13:12 60:01 20:20 292:28 14:15
Mo 10:54 57:14 18:49 66:01 1:56 304:46 15:02
Me 6:13 63:34 13:30 62:51 20:47 296:04 14:34
Ve 4:35 93:02 10:29 42:33 16:23 267:14 11:48
Ma 3:57 103:53 9:20 34:52 14:43 256:17 10:45
Ju 9:24 54:59 17:11 68:33 1:00 305:01 15:36
Sa 1:56 119:18 6:31 24:17 11:06 240:42 9:10
Ur 1:01 123:08 5:24 21:47 9:46 236:52 8:45
Ne 1:14 120:39 5:45 23:24 10:16 239:21 9:02
Pl 19:55 91:11 1:57 43:46 7:55 268:48 12:00
X 1:41 32:26 10:51 81:10 20:00 327:20 18:19
Y 20:08 92:55 2:06 42:29 7:59 267:01 11:50
Move to another field, RETURN to change this field, ? for help, or q to run
CDT 19:00:00 4/30/1990 | LST 8:19:50 | Lat 44:50:37 | April 1990
UTC 0:00:00 5/01/1990 | | Long 93:42:08 | Su Mo Tu We Th Fr Sa
JulianDat 2448012.50000 | Dawn 4:10 | Elev 800 ft | 1 2 3 4 5 6 7
Watch | Dusk 22:15 | Temp 40 F | 8 FM 10 11 12 13 14
Listing off | NiteLn 5:55 | AtmPr 29.50 in | 15 16 17 18 19 20 21
Search off | | TZ 5:00:00 | 22 23 NM 25 26 27 28
Plot off | NStep 1 | Epoch 2000.0 | 29 30
Menu Separations | StpSz RT CLOCK | Pause 0 |
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OCX Sun Moon Merc Venus Mars Jup Sat Uranus Nep Pluto X Y
Su 79:32 4:52 43:59 62:55 56:31 105: 121: 116: 163: 38:21 162:
Mo 79:32 74:49 124: 142: 23:01 175: 160: 164: 106: 99:52 108:
Me 4:52 74:49 48:43 67:39 51:50 110: 126: 121: 163: 39:57 163:
Ve 43:59 124: 48:43 18:56 100: 61:09 77:00 71:58 129: 38:49 126:
Ma 62:55 142: 67:39 18:56 119: 42:14 58:04 53:04 111: 50:48 108:
Ju 56:31 23:01 51:50 100: 119: 162: 177: 172: 128: 80:40 130:
Sa 105: 175: 110: 61:09 42:14 162: 15:52 10:50 69:37 83:36 67:17
Ur 121: 160: 126: 77:00 58:04 177: 15:52 5:11 54:43 97:18 52:21
Ne 116: 164: 121: 71:58 53:04 172: 10:50 5:11 59:06 92:24 56:46
Pl 163: 106: 163: 129: 111: 128: 69:37 54:43 59:06 125: 2:22
X 38:21 99:52 39:57 38:49 50:48 80:40 83:36 97:18 92:24 125: 124:
Y 162: 108: 163: 126: 108: 130: 67:17 52:21 56:46 2:22 124:
- 30 -
Move to another field, RETURN to change this field, ? for help, or q to run
CDT 19:00:00 4/30/1990 | LST 8:19:50 | Lat 44:50:37 | April 1990
UTC 0:00:00 5/01/1990 | | Long 93:42:08 | Su Mo Tu We Th Fr Sa
JulianDat 2448012.50000 | Dawn 4:10 | Elev 800 ft | 1 2 3 4 5 6 7
Watch | Dusk 22:15 | Temp 40 F | 8 FM 10 11 12 13 14
Listing off | NiteLn 5:55 | AtmPr 29.50 in | 15 16 17 18 19 20 21
Search off | | TZ 5:00:00 | 22 23 NM 25 26 27 28
Plot off | NStep 1 | Epoch 2000.0 | 29 30
Menu Jupiter Aux | StpSz RT CLOCK | Pause 0 |
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Central Meridian Longitude (degs): 337.545 (Sys I) 267.021 (Sys II)
(GRS is at approximately 30 degs in System II)
Jupiter Radii
X (+E) Y (+N) Z (+towards)
I Io 0.950 -0.181 -5.808
II Europa -4.052 0.261 8.384
III Ganymede -8.502 0.385 12.350
IV Callisto 26.029 0.160 5.119
G E JI C
West East
