Contents - Index

Target Selection via TheSky


If you are imaging a single target per night, it is best to time your data so that important data occurs near the meridian since you look through the lowest air mass and atmospheric stability will have the least impact on resolution.  One way to assess seeing, the stability of the atmosphere is to visually look at stars from the zenith to lower in altitude.  If you have a reasonably good night, you will see minimal twinkling at the zenith but as you go lower in altitude, the twinkling will begin to appear.  A good night might show twinkling at 45° or so.  If you see twinkling at the zenith, you have a poor night and that might make a good night for acquiring binned data.


Multiple Targets

One way to minimize atmospherics is to take multiple targets with differing transit times over multiple nights.  Using this approach, you can time each target's data to be close to the meridian crossing.  Of course, this requires a reasonable run of clear nights and may not be appropriate for all locations.


Target Location

Ultimately, target location has to consist of Right Ascension (RA), Declination (Dec) and Position Angle (PA).  This defines a position in the sky and a rotation of the camera.  RA and Dec are to be given in J2000 equinox data for consistency.  Any precession to the current equinox is handled by CCDAutoPilot.  Once the target coordinates are defined, they can be entered into CCDAutoPilot via a number of techniques.  See the Targets page command summary for details.

If you have TheSky6 or TheSkyX, a nice way to enter target coordinates is via the Field of View Indicator (FOVI).  Here are the steps to do that. TheSkyX is being used for the screen shots but the technique is applicable to both TheSky6 and TheSkyX.


Target Selection via TheSky

By combining the power of CCDAutoPilot and TheSky6, target planning an acquisition becomes immensely easier.  No more image links or plate solving or trial and error.  All that is required is TheSky and an accurate Field Of View Indicator (FOVI).  All that is needed is to orient the FOVI appropriate to your situation and use a precision slew to target as part of your session.  The coordinates will be precisely arrived at by the mount and, if you have a rotator, it will rotate to the appropriate position angle (PA) automatically.  Here is an example.

Assume you want to image M33.  Here is what you might see in TheSkyX:




Note M33 is located the left edge of the FOVI.  Note the two squares that are part of the FOVI.  Clicking and dragging on the center one translates the FOVI; clicking and dragging the lower one in a circle rotates the FOVI.  First I will translate the FOVI to a position that includes M57 and a guide star is somewhere between the two circles.




I have moved the FOVI off-center to frame M33.   and there is a suitable guide star at the 11 o'clock position.   I'll click on the upper square to rotate the FOVI until the guide star falls on the guider FOVI.




The guider FOVI now includes the guide star.  TheSky indicates a position angle of 220.13 degrees.  By hovering the cursor over the guide star, I see information about the magnitude of the guide star.  This guide star is more than suitable for this image.  The next step is to use this information as a target for CCDAutoPilot.  With CCDAutoPIlot linked to TheSky, all that is required is to hit the Get button on the Targets page with no entry in the field.  The RA and Dec of the center of the FOVI and its position angle will be automatically transferred to the Targets List as shown below.




Note the coordinate information is now in the Target list with the non-unique name "FOV Center".  Double-clicking on the box with "FOV Center" brings up an edit window so you can change the target name to something more descriptive - like M33!  After hitting OK on the Rename Target window, the target row now becomes:





I have now completely described the position of the target for CCDAutoPilot.  When this target is selected for running, the telescope will slew to the target, rotate the rotator as needed to match the PA of 220.1, plate solve and adjust the telescope pointing so that it is within a few arc-sec. of the desired target.  Since guider calibration is no longer necessary with the automatic calibration algorithm of CCDAutoPilot, guided imaging can now begin at this location.

This same technique can be repeated as many times as required for an evening's imaging session.  You do not need to be connected to the actual telescope or camera hardware, just be connected to TheSky.  You can plan an entire evening's imaging away from the telescope and, when you are later connected to your telescope and camera, focuser and rotator if used, begin imaging.  You can be sure imaging will proceed as planned.


For those without a rotator...

You can use much of the same technique described above but with some modification. If you do not have a rotator, there are two choices.  Either frame the target as best you can with translation only or manually rotate the camera to the desired PA, 220.1 in the above example. As long as you have initialized the system at any rotation angle, CCDAutoPilot will automatically determine the needed calibration vectors for your autoguider.