

                            ASTROMETRICA SHAREWARE
                           


 This is an  unclicensed version of  "Astrometrica".  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 so,
 send at least US$ 25.- to the author of  "Astrometrica"  and you will get a
 licensed copy of the latest version of this shareware.

 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 the latest version of "Astrometrica", too.

 It is expressly welcome to distribute copies of this demo disk on diskette,
 via bulletin boards or computer networks.

 The licensed version of  "Astrometrica"  offers  the  following  additional
 functions, disabled in this unlicensed copy:

 * Up to  ten reference stars can be selected,  whereas  an  unlicensed copy
   allows the selection of four stars only.

 * Determination  of the  brightness  of the object  of interest,  using the
   'Measure Position & Mag' command.

 * Comparison of two CCD-images by electronically blinking them.

 * Calculation of ephemeris for the end of evening twilight or the beginning
   of morning twilight, and a "what's up" function.

 The address of the author, where you can order licensed versions of "Astro-
 metrica", is:

                                 Herbert Raab
                                Schrammlstr. 8
                                 A-4050 Traun
                                   Austria
                                   
                                   e-mail:
                         Herbert.Raab@jk.uni-linz.ac.at


 The following documentation  refers to the full version of  "Astrometrica".
 Some of the functions are therefore  not  available when using a unlicensed
 shareware-version.




                               ASTROMETRICA 2.1
                              


  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, supported the comparison
  of two CCD images by electronically blinking them. The method used to dis-
  playing  CCD images was improved,  and the access to  GSC regions has been
  sped up, too.

  A major step is  Version 2.0,  which was finished in April, 1994:  Besides
  some small,  but nevertheless useful features, it was, for the first time,
  possible to use images from  CCD cameras other than the ST-6,  as  it  was
  able to read ST-4 and TIFF files. Furthermore, the methods for astrometric
  and photometric data reduction have been improved.

  Version 2.1,  released in October 1994,  is even more flexible as  it  can
  read ST-4X and FITS  files.  Among  the  many  improvements  is  a  blink-
  comperator that works with images that are rotated against each other  and
  thus makes it possible to compare images taken during different  observing
  session, and an improved centeroiding algorithm.


  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),  version 1.0 or
    1.1,  on CD-ROM or copied onto the computer's hard disk (with  the  same
    directory structure as on the CD-ROM). "Astrometrica"  won't  work  with
    truncated or compressed versions of  the  GSC,  as  shipped  with  other 
    software packages.
    The two GSC CD-ROM's are available from the following adress  for  about
    US$ 70.- + shipping & handling:

            Astronomical Society of the Pacific
            390 Ashton Ave.
            Dept. AD
            San Francisco, CA 94112      U.S. Phone: (415) 337 2624
            U.S.A.                       U.S. Fax:   (415) 337 5205


  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.

  * README.BAT and README.TXT: The text you are reading  and a batch-file to
    display it.

  * LIESMICH.BAT and LIESMICH.TXT: The german version of this text and a the
    batch-file to display it.

  * CCD:  A subdirectory with some sample images and a text file, containing
    some comments to these images.

  * ELM:  A subdirectory  with the orbital elements  of the objects  on  the
    sample images.


  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
  directory to operate from and then copy the files from your "Astrometrica"
  floppy disk onto your hard disk.  You may also  copy the sample images and
  the orbital elements to the subdirectories where you store your CCD images
  and orbital elements, respectively.

  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
  

  ͻ
   Menue    Command           Description                               
  ͹
   File     Load Image        Load,  depending  on  the  configuration, 
                              ST-4, ST-6, TIFF or FITS files from  disk 
                              into the main memory.                     
           Ķ
            View Text-File    Load and display a text-file.             
           Ķ
            Print             Prints the contents of the active Window. 
           Ķ
            Change Dir        Change the default directory.             
           Ķ
            DOS Shell         Temporarily exit to DOS.                  
           Ķ
            Exit              Exit "Astrometrica".                      
  Ķ
   Display  Chart             Display a chart of a part of the sky.     
           Ķ
            Image             Display  the  current  image and  inspect 
                              it's pixel with a crosshair.              
           Ķ
            Parameters        Display information on the current image. 
           Ķ
            Negative          Toggle negative display of the CCD image. 
           Ķ
            Load User         Load and set a ST-6 color table.          
            Color Table                                                 
           Ķ
            Set Standard      Set the standard color table.             
            Color Table       (Gray-scale)                              
  Ķ
   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 brightness 
                              of the object in question.                
           Ķ
            Measure Position  Display  the current  image  in  order to 
                              measure  the  position of  the  reference 
                              stars and the object in question.         
           Ķ
            Measure           Display  the current  image  in  order to 
            Position & Mag    measure the position  and  brightness  of 
                              the  reference  stars  and  the object in 
                              question.                                 
           Ķ
            Remeasure Object  Remeasure the object  without remeasuring 
                              the reference stars.                      
           Ķ
            Information       Display information  on the last measure- 
                              ment  like  plate  constants,  centeroid, 
                              contrast index and focal length.          
  Ķ
   Utility  Scale             Scale  the  image  so  that  a  specified 
                              percentage  of  pixels appear  black (Low 
                              Limit) and white (High Limit).            
           Ķ
            Smooth            Apply a mean value filter to the image.   
           Ķ
            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.              
           Ķ
            Blink Images      Compares two images by blinking them.     
           Ķ
            Edit Parameters   Edit  information  on the  image which is 
                              important  for  astrometric  work.   This 
                              function  will  also  be called  after an 
                              image has been loaded from the disk.      
  Ķ
   Ephem    Load Elements     Load orbital elements  from the disk into 
                              the main memory.                          
           Ķ
            Save Elements     Save the current set of  orbital elements 
                              to disk.                                  
           Ķ
            Discard Elements  Remove the  current orbital elements from 
                              the main memory.                          
           Ķ
            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.            
           Ķ
            Scan Elements     Scan the orbital elements on the disk and 
                              display a "what's up tonight" listing.    
           Ķ
            Display Elements  Displays the current set of elements.     
           Ķ
            Edit Elements     Edit orbital elements.                    
  Ķ
   Options  Directories       Set paths  for the  CCD images,  GSC-data 
                              and ephemeris-files.                      
           Ķ
            Observatory       Set default  information on the  location 
                              and equipment of the observatory.         
           Ķ
            CCD               Set default information on your CCD.      
           Ķ
            Delta T           Set the default value for  T = TDT - UT, 
                              used while calculating an ephemeris.      
           Ķ
            User              Set default information on the user.      
  Ķ
   Windows  Resize/Move       Change the size or position of the active 
                              window.                                   
           Ķ
            Zoom              Enlarge or restore the size of the active 
                              window.                                   
           Ķ
            Next              Make the next window active.              
           Ķ
            Close             Close the active window.                  
           Ķ
            Tile              Arrange windows by tiling.                
           Ķ
            Cascade           Arrange windows by cascading.             
  Ķ
   About    About             Display information about "Astrometrica". 
            Astrometrica                                                
           Ķ
            License Info      Display license information.              
  ͼ


  USING "ASTROMETRICA"
  

  Setup
  

  When you use  "Astrometrica"  for the first time, you should go trough the
  'Options'-menue at first. The 'Directory'-subcommand allows you 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 can 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 'CCD'  submenue  allows you  to specify weather you want to use  ST-4,
  ST-6, FITS or TIFF files. The spectral band in which your CCD camera works
  can also be selected here.  While many CCDs  (like the ST-4 and ST-6)  are
  most sensitive for red light when you don't  use  filters,  a  sensitivity
  for visual light would be desireable,  as the magnitudes  given by the GSC
  are V-magnitudes.
  If you use a camera other than the ST-4 or ST-6, you should also enter the
  pixel size  and the focal length  of the telescope you use. If your camera
  supports different resolution modes,  please enter  the  (apparent)  pixel
  size you use.
  Do the images appear upside-down after  loading  FITS  files,  toggle  the
  'Upside Down' selector.

  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 name you enter here (the surname, at least)
  should be equal to that of the licensee. Otherwise,  a message will appear
  every time you start the program, saying that this copy is not licensed to
  this user.


  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.


  Printing Files and Star Charts
  

  By issuing the  'File - Print' command,  the  contents  of  the  currently
  active window may be printed. However, no contol codes will be sent to the
  printer. Therefore, the user has to activate  the  desired  printer  font.
  Above all, make sure that a condensed font is used when printing ephemeris
  generated with "Astrometrica".

  Printing of graphics is  not supportet by that command.  However,  if  you
  want to print the GSC star charts drawn by  "Astrometrica",  you just have
  to load the memory resident DOS-program "GRAPHICS".  Then,  you  can print
  the star charts by simply hitting the <Print Screen> key.
  Please refer  to your  DOS manual  for the details on how to configure the
  "GRAPHICS"-tool to support your printer.


  Loading Images
  

  Using the 'Load Image'-command from the File-menue,  you can load the CCD-
  images you want to measure.  "Astrometrica" 2.1 reads ST-4, ST-4X and ST-6
  images,  FITS  (8, 16 and 32 bit integer files)  and  uncompressed  8  bit
  gray-scale  TIFF  images.  After  the  image  has  been  loaded,  the most
  important  parameters  (Date,  Universal  Time  of  mid-exposure  and  the
  observer's name) will be displayed and may be changed, if neccessary.

  With sufficient memory,  it is possible to load FITS and TIFF images up to
  512 x 256 pixels in size. Even larger images, up to 1024 x 512 pixels, can
  be read.  Then, four pixels will be combined internally in order to divide
  the image dimensions in half.

  * ST-4 Images:
  The ST-4 file does not give  any information on the date and time when the
  exposure was made. Only the comment string, which, however, may be changed
  by the user, usually holds the information when the exposure ended.
  "Astrometrica"  therefore tries to isolate date and time from this string.
  By substracting  half the exposure time,  the time of mid-exposure will be
  calculated.

  * ST-4X and ST-6 Images:
  The header of  SBIG files  gives information  on the time of the start and
  the duration of the exposure.  "Astrometrica"  can therefore calculate the
  time of mid-exposure by adding half the exposure time to the time when the
  exposure was started.
  However, when loading an image taken with the SBIG 'Track and Accumulate'-
  mode, this method fails: 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!

  * FITS Images:
  As there is a 'DATE-OBS' keyword defined by the FITS standard, the date of
  the observation can usually be read from  the  FITS-header.  Please  note,
  however, that the date shall be given as  DD/MM/YY. Many software products
  incorrectly use the format MM/DD/YY instead.  Therefore, watch out for in-
  correct dates!
  When encountering a 'TIME-OBS' keyword,  "Astrometrica"  adopts  the  time
  given there as the time of mid exposure. When both the keywords 'TIME-BEG'
  and 'TIME-END' are included in the FITS header, the program calculates the
  time of mid-exposure by averaging the two times given.

  * TIFF Images:
  As the TIFF format was  not designed  for  astronomical  applications,  it
  gives no information on  when the image was taken.  The user has therefore
  to enter date and time manually.

  If you have the choice between  TIFF  and  FITS images (when using cameras
  other than the ST-4 or the ST-6), always use the FITS format.

  CAUTION!!
  ALWAYS check the  date and Universal Time (UT)  of mid-exposure carefully,
  no matter what camera you use!  Remember that this time should be accurate
  to one second!


  Displaying images
  

  The  'Display - Image'  command  may  be  used  to display the current CCD
  image.  Furthermore, it is possible to obtain pixel data using crosshairs:
  Below the image,  the  coordinates  of  the pixel where the crosshairs are
  located,  as well as the saturation of this pixel in percent, will be dis-
  played.  The  crosshairs can be moved using the cursor keys, or by a mouse
  click.


  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 high pass filters  ('Sharpening'-
  filters),  unsharp masking or convolution methods may modify  the image in
  a way that the calculation of the centeroid of an image is influenced.

  Scaling of images may influence the results, too. Linear scaling (which is
  necessary to create 8 Bit TIFF images from 16 Bit image data, for example)
  does not much harm,  when  you try  not to loose  much information.  Other
  methods,  like  logarithmic scaling,  should not be used on the images you
  want to measure.

  The scaling function of  "Astrometrica",  by the way,  does not change the
  values of the  pixels in the image,  and therefore may be used  safely. It
  just sets the display parameters (background and range)  so that the image
  may be viewed at optimum contrast.

  In general, try using unfiltered and unscaled images for astrometric work.


  Compare Images
  

  By using the 'Blink Images' command of the 'Utility' menu,  two 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
  two reference points (bright stars, for example)  on both images by click-
  ing on them, so the images can be aligned. To make exact aligments easier,
  the mouse cursor may also be moved by pressing the arrow keys.

  If the two images are not rotated against each other (e.g., the camera has
  not been removed  from the telescope in the time between the images),  the
  selection of a single reference point in each image is sufficient. Instead
  of  selecting  the second reference  point  on the first image,  press the
  <Esc> key in that case.

  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 any 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 time  stored with the CCD 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,  where the aspect ratio of
  the chart  will be set  to  fit  that  of  the CCD image.  If there are no
  orbital elements 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.

  You can also select reference stars from a chart  drawn after you selected
  the  'Display - Chart'  command.  You have to care for the  coordinates of
  the field then. While the computer gives you a suggestion for the scale of
  the chart to fit the CCD image,  the aspect ratio of the chart will not be
  changed to fit the CCD image.

  Select reference stars,  which are neither under-  (hardly distinguishable
  from  the background noise)  nor over-exposed  (with a saturation of 100%,
  or,  in other words,  with a pixel-value  of 65535 for 16 bit images).  If
  possible, select seven to ten reference stars which are evenly distributed
  around the object.


  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 to 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 over-
  exposed (e.g. with a saturation of 100%).

  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 arrow keys  are used to move this box,  and a mouse click can
  move the box  over a larger distance  to the location of the mouse cursor.
  The function keys  F1..F4  may be used to change the size of the box,  the  
  keys  F5..F7  can be used to change image contrast,  and the F8 key may be 
  used to display a zoomed image section:

    F1: Decrease x-size of box.
    F2: Increase x-size of box.
    F3: Decrease y-size of box.
    F4: Increase y-size of box.
    F5: Boost image contrast. Makes faint regions easier to see.
    F6: Restore original contrast.
    F7: Scale the image in a way that the gray levels are evenly distributed
        among that part of the image which lies inside the cursor box.
        If the image still appears too bright, use a smaller box  and  scale
        the image again. Is the image too faint, use a larger box.
    F8: Display a zoomed section of  the  image,  centered  on  the  current 
        position of the cursor box.  A dotted cross indicates the  centeroid 
        as calculated by the software.

  A small window  displayed  below  the  image  gives you information on the
  location of the box (x,y coordinates), the saturation of the central pixel
  in percent, and the boxsize.

  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 do
  so, move the box to a large 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.

  The background value is substracted  from each pixel  when calculating the
  magnitude  and position of the reference stars and the object.  If you re-
  scale the image using the F7 or F8 key,  the maximum of the measured back-
  ground and the background value used for displaying the image will be used
  for the centeroid calculation.  This simply means that  what you don't see
  has no effect on the centeroid calculation.

  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.  If the faint,
  outer region  of a comet's coma  has not been recorded  because of a short
  integration time,  the magnitude  of the comet  may be under-estimated  by
  several magnitudes!

  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 by using the scaling function (F7 key).

  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 completed,  the positions and magnitudes of
  the reference stars  and the object will be calculated.  The brightness is
  calculated  from a linear regression  between the measured intensities and
  the intensities calculated from the entries in the GSC. Using the measured
  positions of the reference stars,  the plate constants a, b, c, d, e, f, g
  and h will be calculated. With their help, it is possible to calculate the
  rectangular standard coordinates X and Y from the measured positions x and
  y in the following way:
                          X = a*x + b*y + c*xy + d
                          Y = e*x + f*y + g*xy + h

  In case you have measured only four reference stars, the plate constants c
  and g are set equal to zero. From the rectangular standard coordinates, it
  is finally possible  to calculate the spherical coordinates of the objects
  we are looking for.

  After the calculations described above have been finished, the  results of
  the data reduction  will be  displayed.  For each reference  star  and the
  object of interest, the measured position and, eventually,  the  magnitude
  will be shown. For the reference stars, the O-C (observed-calculated)  re-
  siduals 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 residuals 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. But the motion
  of the true object and that of a hypothetic object on the given orbit  can
  be considered as parallel for the short period of time between the  images
  of the object taken during one observing session.  The  scatter  of  these
  values therefore gives a hint on the quality of the measurements.

  The results of the measurement will be summarized in the files REPORT.TXT,
  CREPORT.TXT and ASTROMET.LOG.

  If your image shows more than one minor planet, or if you want to measure,
  for example,  a comet using both a 7 x 7 and a 9 x 9 box,  you may use the
  'Remeasure Object' command, which allows you to measure the object without
  having to measure the background and the reference stars, again.

  If you measure different objects using the 'Remeasure Object' function, do
  not forget to load the corresponding orbital elements, if you want to com-
  pare your results with the ephemeris.


  Results
  

  Since the beginning of its developement,  "Astrometrica"  has been used by
  the author and his  collegue  Erich Meyer.  Using a ST-6 CCD camera on the
  Schmidt-Cassegrain telescope  (288mm diameter, 1500mm focal length) of the
  private observatory Obermair/Meyer, which lies near Linz, Austria, Europe,
  at 48.4425 northern latitude, 14.2753 eastern longitude,  815m above the
  sea level, over 750 precise positions of comets  and  minor  planets  have
  been measured betwenn March 1993 and October 1994. These observations have
  been published regularly in the Minor Planet Circulars  under  the  obser-
  vatory code 540,  and  sometimes  also  in  the  Minor  Planet  Electronic
  Circulars or the IAU Circulars.

  Although the pixel size is 3.2" x 3.7" at the focal length of 1500mm,  the
  mean  residual  of the reference  stars  has setteled  near  0.2"  per co-
  ordinate.  However, these residuals are minimized by the least square fit.
  Furthermore,  there are systematical errors within the GSC.  Therefore, we
  may expect higher residuals for the objects we measure.  But how large are
  these errors?

  During 1994, the Minor Planet Center published the  O-C  residual  of  129
  observations of minor planets 1993 UC,  1993 WD,  1994 AH2  and  1994 EQ3,
  made at Linz with the equipment described above.  Of  these  observations,
  29% had a total residual of 0.5" or less, 50%  had  a  total  residual  of
  0.7" or less, 71% had a total residual of 1.0" or less and 85% had a total
  residual of 1.5" or less. Only a single observations had a total error  of
  more than 2.0", namely 3.2" - still less than the size of a pixel.

  These results are possible  due  to  the  calculation  of the centeroid of
  light. Furthermore,  "Astrometrica"  makes use of an algorithm to disting-
  uish the pixels that form the image to be measured  from  the  background.
  Note that the results given above were obtained before the  new,  improved
  centeroiding algorithm of "Astrometrica" has been implemented.

  Note that, for optimum performance, the images  of the stars  must cover a
  minimum amount of pixels.  A short focal length  or  extremly  sharp  star
  images will therefore negatively influence the results.  While unfavorable
  observing conditions, like moderate seeing  or  light pollution,  decrease
  your limiting magnitude, they do hardly harm the  quality  of  astrometric
  measurements.

  In order to get the best results from your images, keep these simple rules
  in mind:

  *  Measure your images only after you have substracted the dark frame  and
     after you have applied the flat-field correction only.

  *  Try to use 7 to 10 reference stars,  roughly equally distributed around
     the object of interest.  The  images of the  reference stars  should be
     neither noisy, nor satured.  Furthermore,  try to use  reference  stars
     which have no close companions.

  *  Try to locate  the center  of the box  for measuring  the images at the
     brightest pixel of the reference star or object.  The  brightest  pixel
     within the box must be part of the image to be measured. Size  the  box
     to fit the object you measure.

  *  Use the image scaling function  (F7 key)  to locate  the nucleus within
     the coma of a  bright comet. You  should  not  use  this  function  for
     ordinary point sources (stars, minor planets),  as  the amount  of data
     used for the centeroid calculation will be decreased.

  *  If the mean residual of the reference star position is much larger than
     you might expect (larger than 1") you either have used a telescope with
     too short a focal length (say, less than 500mm or so), or you have mis-
     identified at least one of the reference stars.
     In the latter case, make sure that your identification of the reference
     stars is correct, and measure the image again.

  *  If  the  measured  magnitude  of the  object seems to scatter more than
     usual, or if it seems to be much too faint, the signal/noise ratio  may
     be too low. Try to use longer exposure times or to co-add some images.

  *  The  'Measure - Information'  command  gives  you  information  on  the
     quality  of  the  object's  image  just  measured.   Images  with  mean
     intensities under 3 are too faint to get relieable data from.  Is  the
     image of the object fainter than that criteria,  or  does  it  cover  a
     small number of pixels only, try using longer  exposure  times  or  co-
     adding some images.

  *  Watch out  for  unusually large scatter of the  "O-C Residuals"  of the
     object, which will be displayed if you have the orbital elements loaded
     when measuring the image.


  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.

  Airmass ....... Length of the path of the light trought earths atmosphere,
                  in units of airmasses at the zenith. The starlight will be
                  dimmed by about 0.23mag per airmass-unit.

  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.

  , 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.)

  The results  of the ephemeris calculation  will be saved in the file named
  'EPHEM.TXT'.  By using the 'File - Print' command,  it is possible to send
  the file to the printer. Keep in mind that the text in this file has up to
  121 characters per column, so the user has to activate a condensed printer
  font before printing the file.


  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.  (CREPORT stands for Computerized Report.)  In this format,  the
  object is  identified  by a short name,  which you can enter  when editing
  orbital elements. Here are a few examples (most are taken from the October
  1991 M.P.C.s) which illustrate how to use the short name:

  Name:   [Ceres     ] [00001     ]  --  Minor Planet (1) "Ceres"
                                         Five digits, note the leading
                                         zeros!

  Name:   [1990HV4   ] [J90H04V   ]  --  Minor Planet 1990 HV4
                                         J for century digit 19

  Name:   [2000YZ109 ] [K00YA9Z   ]  --  Minor Planet 2000 YZ109
                                         5th digit A for 10

  Name:   [P/Halley  ] [J8603J820i]  --  Comet 1986III = 1982i "P/Halley"

  Name:   [1988 XVIII] [J8818J871c]  --  Comet 1988 XVIII = 1987c1

  Name:   [1993e     ] [J930e     ]  --  Comet 1993e "P/Shoemaker-Levy 9"
                                         No definite designation yet

  Name:   [P/Encke   ] [J9021    `]  --  Comet 1990XXI "P/Encke"
                                         No provisional designation
                                         ` marks a comet

  Take care to enter the short name correctly!

  Please note  that the name of the object will be written to the REPORT.TXT
  and  CREPORT.TXT files only if you have the orbital elements of the object
  loaded while measuring its position.  (The center of the chart for select-
  ing reference stars and the  "O-C residuals"  for the object  will also be
  calculated by the computer in that case.)


  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  modern CCDs   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
