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ASTROMETRICA SHAREWARE
════════════════════════
This is a shareware-version of "Astrometrica", with roughly the same
functions as the first few test-versions of "Astrometrica": It can
calculate ephemeris, display star charts based on the "Hubble Space Tele-
scope Guide Star Catalog" and measure astrometric positions from ST-4 and
ST-6 CCD-images. Later improvements of these functions, like the ability
of loading compressed ST-6 files, have been taken over.
The full version of "Astrometrica" offers the following additional
functions:
* Simultane display of a CCD-image and the corresponding star chart in
order to simplify the selection of reference star. Position and size of
the starchart will be calculated automatically according to the image-
data and the orbital elements.
* Determination of the brightness of the object of interest.
* Tools for scaling and filtering CCD-images.
* Comparison of two CCD-images by electronically blinking them.
* Calculation of ephemeris for the end of evening twilight or the beginning
of morning twilight.
As usual, you may use this shareware two weeks for free. After you have
tested this software, you either delete all copies, or register yourself
as licensed user. To do this, send US$ 25.- to the author of "Astrometrica"
and you will get a licensed copy of the program.
As a shareware author, you may use the program for free, but you should
contact the author of "Astrometrica", too: After sending a description of
your shareware-programs to the address given below, you will receive a
licensed copy of "Astrometrica".
The address of the author, from where you can also order full versions of
"Astrometrica", is:
Herbert Raab
Schrammlstr. 8
A-4050 Traun
Austria
The following documentation refers to the full version of "Astrometrica".
Some of the functions are therefore not available for users of the share-
ware-version.
ASTROMETRICA 1.2
══════════════════
ABOUT ASTROMETRICA
══════════════════
"Astrometrica" 1.0 was implemented between February and June 1993 in
order to check the possibility of using CCD-cameras for astrometric work
on minor planets and comets.
During the developement of "Astrometrica", in the months mentioned above,
about 150 CCD-images of comets were measured successfully. Thus, it was
possible to adapt the program to the needs of practical working amateurs.
Version 1.1 was created in September 1993. It allowed loading compressed
ST-6 files and writes, besides the conventional REPORT file, a file named
CREPORT, which is compatible to the standard format given on M.P.C. 18847
to 18849 (October 1991). This file may be used for sending astrometric
observations via computer networks or on diskette.
Version 1.2, which was released in October 1993, supports the comparison
of two ST-6 CCD-images by electronically blinking them. The method used
for displaying ST-6 images was improved, and takes now only about 40% of
the time when compared to older versions. The access to GSC regions has
been sped up, too.
WHAT YOU NEED
═════════════
* PC-compatible computer with 80286 (or later) CPU, standard VGA graphics
card, Microsoft-compatible mouse, and 512kB free memory.
* MS-DOS 3.3 (or later version).
* The "Hubble Space Telescope Guide Star Catalog" (GSC) on CD-ROM or
copied onto the computer's hard disk, with the same directory structure
as on the CD-ROM.
The two GSC CD-ROM's are available from the following adress:
Astronomical Society of the Pacific
HST Orders Dept.
390 Ashton Ave.
San Francisco, CA 94112
* SBIG's ST-6 CCD camera and the ST6OPS software.
* A telescope having a focal length between about 1000mm and 3000mm.
While the field of view may be too small to find enough reference stars
when using longer focal lengths, the image scale may be to low to derive
accurate positions when using shorter focal lengths.
WHAT'S ON THE DISK
══════════════════
The diskette holds the following files:
* ASTROMET.EXE: The executeable "Astrometrica"-program.
* REGIONS.DAT: A file which holds information on the location of the GSC-
regions.
* ST4TO6.EXE: A tool to convert ST-4 images into ST-6 file format.
* README.BAT und README.TXT: The text you are reading and a batch-file to
display it.
* LIESMICH.BAT und LIESMICH.TXT: The german version of this text and a the
batch-file to display it.
INSTALLING ASTROMETRICA
═══════════════════════
Installing "Astrometrica" on your computer's hard disk drive is very
simple. Using the MS-DOS command MD (for Make Directory), create a
driectory to operate from and then copy the files from your "Astrometrica"
floppy disk onto your hard disk.
When you start "Astrometrica" for the first time, a message will appear
telling you that the file for initializing the software could not be
found. You should go trough the 'Options'-menue now and configure the
sofware, as described later.
COMMANDS
════════
╔═════════╤══════════════════╤═══════════════════════════════════════════╗
║ Menue │ Command │ Description ║
╠═════════╪══════════════════╪═══════════════════════════════════════════╣
║ File │ Load Image │ Load an uncompressed ST-6 image from the ║
║ │ │ disk into the main memory. ║
║ ├──────────────────┼───────────────────────────────────────────╢
║ │ View Text-File │ Load an display a text-file. ║
║ ├──────────────────┼───────────────────────────────────────────╢
║ │ Change Dir │ Change the default directory. ║
║ ├──────────────────┼───────────────────────────────────────────╢
║ │ DOS Shell │ Temporarily exit to DOS. ║
║ ├──────────────────┼───────────────────────────────────────────╢
║ │ Exit │ Exit "Astrometrica". ║
╟─────────┼──────────────────┼───────────────────────────────────────────╢
║ Display │ Chart │ Display a chart of a part of the sky. ║
║ ├──────────────────┼───────────────────────────────────────────╢
║ │ Image │ Display the current image. ║
║ ├──────────────────┼───────────────────────────────────────────╢
║ │ Parameters │ Display information on the current image. ║
║ ├──────────────────┼───────────────────────────────────────────╢
║ │ Load User │ Load and set a color table. ║
║ │ Color Table │ ║
║ ├──────────────────┼───────────────────────────────────────────╢
║ │ Set Standard │ Set the standard color table. ║
║ │ Color Table │ (Gray-scale) ║
╟─────────┼──────────────────┼───────────────────────────────────────────╢
║ Measure │ Select Reference │ Display a chart of that part of the sky ║
║ │ Stars │ seen on the CCD-image in order to select ║
║ │ │ the reference stars, which will be used ║
║ │ │ to calculate the position and/or bright- ║
║ │ │ ness of the object in question. ║
║ ├──────────────────┼───────────────────────────────────────────╢
║ │ Measure Position │ Display the current image in order to ║
║ │ │ measure the position of the reference ║
║ │ │ stars and the object in question. ║
║ ├──────────────────┼───────────────────────────────────────────╢
║ │ Measure │ Display the current image in order to ║
║ │ Position & Mag │ measure the position and brightness of ║
║ │ │ the reference stars and the object in ║
║ │ │ question. ║
╟─────────┼──────────────────┼───────────────────────────────────────────╢
║ Utility │ Scale │ Scale the image so that a specified ║
║ │ │ percentage of pixels appears black (Low ║
║ │ │ Limit) and white (High Limit). ║
║ ├──────────────────┼───────────────────────────────────────────╢
║ │ Smooth │ Apply a mean value filter to the image. ║
║ ├──────────────────┼───────────────────────────────────────────╢
║ │ Median Filter │ Apply a median filter to the image. This ║
║ │ │ removes speckles and noise just as the ║
║ │ │ mean value filter does, but without ║
║ │ │ sacrificing image sharpness. ║
║ ├──────────────────┼───────────────────────────────────────────╢
║ │ Blink Images │ Compares two images by blinking. ║
║ ├──────────────────┼───────────────────────────────────────────╢
║ │ Edit Parameters │ Edit informationn on the image which is ║
║ │ │ important for astrometric work. This ║
║ │ │ function will also be called after an ║
║ │ │ image has been loaded from the disk. ║
╟─────────┼──────────────────┼───────────────────────────────────────────╢
║ Ephem │ Load Elements │ Load orbital elements from the disk into ║
║ │ │ the main memory. ║
║ ├──────────────────┼───────────────────────────────────────────╢
║ │ Save Elements │ Save the current set of orbital elements ║
║ │ │ to disk. ║
║ ├──────────────────┼───────────────────────────────────────────╢
║ │ Discard Elements │ Remove the current orbital elements from ║
║ │ │ the main memory. ║
║ ├──────────────────┼───────────────────────────────────────────╢
║ │ Calculate │ Calculate an ephemeris from the current ║
║ │ │ set of orbital elements for a given time, ║
║ │ │ at the end of evening twilight or the ║
║ │ │ beginning of morning twilight. ║
║ ├──────────────────┼───────────────────────────────────────────╢
║ │ Display Elements │ Displays the current set of elements. ║
║ ├──────────────────┼───────────────────────────────────────────╢
║ │ Edit Elements │ Edit orbital elements. ║
╟─────────┼──────────────────┼───────────────────────────────────────────╢
║ Options │ Directories │ Set paths for the CCD-images, GSC-data ║
║ │ │ and ephemeris-files. ║
║ ├──────────────────┼───────────────────────────────────────────╢
║ │ Observatory │ Set default information on the location ║
║ │ │ and equipment of the observatory. ║
║ ├──────────────────┼───────────────────────────────────────────╢
║ │ Delta T │ Set the default value for T = TDT - UT, ║
║ │ │ used while calculating an ephemeris. ║
║ ├──────────────────┼───────────────────────────────────────────╢
║ │ User │ Set default information on the user. ║
╟─────────┼──────────────────┼───────────────────────────────────────────╢
║ Windows │ Resize/Move │ Change the size or position of the active ║
║ │ │ window. ║
║ ├──────────────────┼───────────────────────────────────────────╢
║ │ Zoom │ Enlarge or restore the size of the active ║
║ │ │ window. ║
║ ├──────────────────┼───────────────────────────────────────────╢
║ │ Next │ Make the next window active. ║
║ ├──────────────────┼───────────────────────────────────────────╢
║ │ Close │ Close the active window. ║
║ ├──────────────────┼───────────────────────────────────────────╢
║ │ Tile │ Arrange windows by tiling. ║
║ ├──────────────────┼───────────────────────────────────────────╢
║ │ Cascade │ Arrange windows by cascading. ║
╟─────────┼──────────────────┼───────────────────────────────────────────╢
║ About │ About │ Display information about "Astrometrica". ║
║ │ Astrometrica │ ║
║ ├──────────────────┼───────────────────────────────────────────╢
║ │ License Info │ Display license information. ║
╚═════════╧══════════════════╧═══════════════════════════════════════════╝
USING "ASTROMETRICA"
════════════════════
Setup
─────
When you use "Astrometrica" for the first time, you should go trough the
'Options'-menue at first. The 'Directory'-subcommand allows yo to specify
the path where the CCD-images are stored, the CD-ROM-drive where to search
for the GSC-data (or a subdirectory on a hard disk, with the same tree
of subdirectories as on the CD-ROM) and the path where the files holding
the orbital elements are to be found.
The 'Observatory'-subcommand is used to set the default information on the
location and equipment of your observatory, which is used during the
calculation of an ephemeris and the preparation of the REPORT-file.
The 'Delta T'-subcommand allows you to set the value for T = TDT - UT,
which is used while calculating an ephemeris to convert universal time to
dynamical time and vice versa.
The 'User'-Subcommand asks you for your name and your adress, which will
appear in the REPORT-file.
The Status Window
─────────────────
The status window appears on the bottom of the desktop when you start
"Astrometrica". Like other windows, it can be moved around, but you can't
close it. It shows the filename of the image loaded, the filename of the
color table loaded, the filters applied to the current image, the filename
of the current orbital elements, and the number of selected reference
stars held in the computers main memory. In some cases, short messages
appear within the status window.
Loading Images
──────────────
Using the 'Load Image'-command from the File-menue, you can load the CCD-
images you want to measure. The 1.2 version of "Astrometrica" reads ST-6
images of file version 2 or 3 and data version 1. After the image has been
loaded from disk, the most important parameters are diplayed and may be
changed, if necessary. "Astrometrica" calculates the time of mid-exposure
by adding half the exposure time used to the time when the exposure was
started. As these times are taken from the header of the image file, they
depend on the internal clock of the computer that was used while taking
the images.
CAUTION: When loading an image taken with the ST6 'Track and Accumulate'-
mode, the time of mid-exposure can NOT BE CALCULATED CORRECTLY! You have
to calculate the time of mide-exposure manually by averaging the times of
mid-exposure of the individual images.
ALWAYS check the date and universal time of mid-exposure carefully!
Filtering Images
────────────────
The 'Smooth' function and the 'Median Ffilter' can be used to remove
specks in the image or reduce the effects of noise. The smooth function
applies a mean value filter to the image, which sets the gray value of
each pixel to the mean value of the pixel itself and its adjected
neighbours, which blurs the image a bit.
The median filter removes specks and noise without sacrifying sharpness by
setting the gray value of each pixel to the median of itself and its
adjected neighbours. However, it takes about three times longer to
process the image this way as with the smooth function.
Be careful when measuring images processed by filters other than the two
mentioned above! Some filters (such as the high pass filter used by the
'Sharpen' function of the ST6OPS software) may modify the image in a way
that the calculation of the centeroid of an image is influenced. In
general, try using unfiltered and unscaled images for astrometric work.
The scaling function of "Astrometrica", by the way, does not change the
values of the pixels in the image, and therefor may be used safely. It
just sets the display parameters (background and range) so that the image
may be viewed at optimum contrast.
Compare Images
──────────────
By using the 'Blink Images' command from the 'Utility' menu, two ST-6 CCD-
images can be compared, in order to detect moving or variable objects.
First, the file holding the comparison image must be selected. Then you
have to mark a reference point (a bright star, for example) on both images
by clicking on it, so the images can be aligned.
For comparison, the images will be displayed alternately. The time each
image will be displayed can be controlled by the keys '0' to '9', where
pressing the key '1' means that each image will be displayed for 50ms,
while it will be displayed for 450ms when you press '9'. After pressing
'0', each image will be displayed until the user allows switching by
pressing a key.
Pressing the Escape-key exits the blinking procedure.
Selecting Reference Stars
─────────────────────────
By issuing the 'Measure - Select Reference Stars' Command, you can select
the reference stars, whose data from the GSC are later used to calculate
the position and brightness of the object in question.
From the data stored with the ST-6 image and from orbital elements, the
computer is able to select the region of the sky so that the chart and the
CCD-image can be displayed at the same scale. If there are no orbital ele-
ments loaded, the user has to enter the position of the object at the time
the image was taken.
If you have rotated the camera so that north is not up in the image, you
can compensate this field Rotation, so the cahrt and the CCD-image may be
displayed with the same orientation.
The field of view given should not be changed, if the focal length of the
telescope is set correctly by the 'ST6OPS'-Software, because the computer
positions the box, which is used to measure an image, according to the po-
sitions of the selected stars on the chart.
You can also select reference stars from a chart drwan after you selected
the 'Display - Chart' command. However, you have to care for the co-
ordinates and the size of the field then.
Measuring an image
──────────────────
Before you use CCD images for astrometric purposes, substract the dark
frame and apply the flat field correction to the image. It should be
possible display the image in a way that the stars and the object you want
to measure appear on a uniform, dark background. Otherwise, a longer
integration time may be necessary. On the other hand, neither the
reference stars nor the object you want to measure should be overexposed
(e.g. with a pixel-value of 65535).
After selecting the 'Measure Position'- or 'Measure Position & Mag'-
command, the current CCD image will be displayed and a box, which is used
to measure the position and magnitude of the stars on the image, will
appear. The size of this box may be changed using the keys F1 to F4, so
it will fit the images of the objects to be measured: Using the F1 and F2
keys, the x-size of the box can be decreased and increased, respectively,
while the F3 and F4 keys can be used to decrease and increase the y-size
of the box.
Before the object of interest and the refernce stars can be measured, the
brightness of the backgound-sky has to be determined. In order to to
this, move the box to a region free of nebulae and stars, and press the
Enter key. If the background does not appear uniformly bright, measure the
brightness of the background near the object of interest.
If you have selected the 'Measure Position & Mag'-command, the brightness
of the object of interest will be measured next. Locate the box so that
the object lies completely within this box - including the faint, outer
coma in case of comets - and press the Enter key again.
Then, the position of the object of interest will be measured. Locate the
box so that the centeroid of light lies near the middle of the box. In
case of comets, you may "cut off" the coma and take into account the
nucleus of the object only.
Now, the reference stars will be measured. Locate the box so that the com-
plete image of each star lies within the box. If you have selected the
'Measure Position & Mag'-command, the position and brightness will be me-
asured simultaneously.
After the measurement has been cempleted, the results of the data re-
duction will be displayed. For each reference star and the object of
interest, the measured position and magnitude will be shown. For the
reference stars, the O-C (observed-calculated) residuals for position and
magnitude will appear, too. If you have selected the 'Measure Position'-
command, no magnitudes will be given. The measured pixel coordinates of
each object will be displayed instead.
If there are orbital elements loaded, the O-C residual of the object will
be shown as compared to the ephemeris. In contrast to the residuals given
for the reference stars, this value is not the "true" residual, as you
usually measure the position of the object to refine it's orbit, and thus
the position of the object can not be calculated precisely. However, you
can compare the value given with that for other images of the same object,
taken during the same observing session. This allows you to make a guess
of the quality of the measurements from the variation of the residuals.
The results of the measurements will be summarized in the file REPORT.TXT.
Editing orbital Elements
────────────────────────
After selecting 'Ephem - Edit Elements'from the Menue, you have to decide
weather you want to edit the orbital elements of a comet or a minor
planet. If there is already a set of orbital elements loaded, only the
selection which does not conflict with these elements is possible. Before
you load, or key in, any elements, or after selecting the 'Discard
Elements' command, both selections are possible.
The field asking for the name of the object is split in two parts. The
firts part may be used to enter a name or number for the object, while the
second part may be used to enter a short name (see informations on the
file 'CREPORT.TXT'). In case you don't need the CREPORT-file, which uses a
standard format for reporting astrometric observations, this field may be
left blank.
The orbital elements you key in now may be given for any aequinox: They
will be converted to the standard epoch J2000.0 by the program.
Calculatin an ephemeris
───────────────────────
"Astrometrica" can calculate a detailed ephemeris from orbital elements
keyed in by the user or read from the disk. The ephemeris may be
calculated for a given instance of time, for the end of the astronomical
evening twilight or the beginning of the astronomical morning twilight.
The following information is given:
Date, U.T. .... Date and universal Time for which the following data are
valid.
R.A., Decl. ... Aequatorial coordinates of the object (J2000.0).
Alt, Az ....... Horizontal coordiantes of the object.
El ............ Elongation of the object from the Sun.
Moon .......... Angular distance of the object from the Moon. An asterisk
is printed if the moon is above the horizon at the given
instant.
k ............. Illuminated fraction of the moon's disk in percent.
mag ........... Predicted magnitude of the object.
Ph ............ Phase angle of the object. (For minor planets only.)
Tail .......... Predicted position angle of the ion-tail. (For comets
only.)
r, d .......... Distance of the object to Sun and Earth in Astronomical
Units.
µ, P.A. ....... Appearent motion of the object: Angular speed in arcsec.
per minute, position angle of the direction of motion.
t ............. Period for the motor which is used to compensate for the
motion of the object. (The period at 1"/min may be entered
using the 'Options/Observatory' command.)
Using ST-4 Images
─────────────────
Because of the small size, SBIG's ST-4 CCD-camera is hardly used for
astrometric work. However, if you would like to measure the position of an
object on an ST-4 image, you may convert the ST-4 image to the ST-6 file
format by using the ST4TO6 program supplied with "Astrometrica".
Just start the ST4TO6 program from the DOS command line with the filename
of the image you want to convert as the only parameter. The program will
convert the image to ST-6 file format and save the image using the same
name, but with "ST6" as extension. For example, if you want to convert the
image named "COMET.CCD" to the ST-6 file format, type "ST4TO6 COMET.CCD"
at the DOS promp and press the Enter key. The result of the conversion
will be saved as "COMET.ST6".
It should be noted that the header of ST-4 images does not hold as many
information as the header of ST-6 files. The ST4TO6 converter fills in the
fields where possible. Date and Time, however, are set to the default
value of Jan. 1, 1980, 00:00:00.
The file 'CREPORT.TXT'
──────────────────────
This file holds the data from the astrometric observations according to
the standard format given on M.P.C. 18847 to 18849 (October 1991) and may
be used for sending astrometric observations via computer networks or on
diskette.
To hold this format strictly, keep this in mind: The three-digit observer-
code must be entered right-bound in the corresponding field of the dialog-
window 'Options - Observatory'. Also, the short name of a minor planet
must be entered right-bound, while that of an comet must be entered left-
bound, according to the examples given below, when entering the orbital
elements of the object using the dialog window 'Ephem - Edit Elements'.
Name: [Ceres ] [ 00001] -- Minor Planet (1) "Ceres"
Name: [1993HR4 ] [ J93H04R] -- Minor Planet 1993 HR4
Name: [P/Halley ] [J8603J820i] -- Comet 1986II = 1982i "P/Halley"
Name: [1993e ] [J930e ] -- Comet 1993e "P/Shoemaker-Levy 9"
Name: [P/Encke ] [J9021 `] -- Comet 1990XXI "P/Encke"
Take care to enter the short name correctly!
CREPORT, by the way, stands for Computerized REPORT.
COPYRIGHT
═════════
The copyright and all other rights are owned by the author:
Herbert Raab
Schrammlstr. 8
A-4050 Traun
Austria
"Astrometrica" was implemented using Borland Pascal 7.0 (c).
The user interface is based on Borland's Turbo Vision 2.0 (c).
Brand and product names mentioned in the text are usually trademarks or
registered trademarks of their respective holders.
DISCLAIMER
══════════
"Astrometrica" is supplied as is. The author disclaims all warranties,
expressed or implied, including, without limitation, the warranty of fit-
ness for any purpose. The author assumes no liability for damages, direct
or consequential, which may result from the use of "Astrometrica".
However, I tried hard to write a program which is easy to use and does
what you want it to do. Months of using it have shown that "Astrometrica",
in combination with SBIG's ST-6, is a powerful instrument which gives
amateur astronomers the possibility to do scientific work on minor planets
and comets.
If you have discovered a bug or have any ideas for future releases of this
software, please let me know!
Have fun with "Astrometrica" !
Herbert Raab