Contents - Index

Target Selection

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, a nice way to enter target coordinates is via the Field of View Indicator (FOVI).  Here are the steps to do that.


Target Selection via TheSky6

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 TheSky6 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 M57.  Here is what you might see in TheSky6




M57 is located to the left of the imager FOVI.  The guider FOVI is at 12 o'clock and happens to be positioned over a suitable guide star but that is of no help.  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 and there is a suitable guide star at the 1 o'clock position. 




The guider FOVI now includes the guide star.  TheSky6 indicates a position angle of 138.3.  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 connected to TheSky6, 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 it's 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".  By right-clicking on FOV Center, I can then select the edit menu to change the name to something more descriptive, like M57!




I have entered M57 for the target name.  After hitting OK, the target list looks like this:




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 138.3, 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 TheSky6.  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 connected, and have initialized your system, you will find this entry in the "No Rotator In Use" box:



When you move the FOVI as described above, and assuming the value shown above for Init. PA, you will need to insure your FOVI PA is 234.1 if the target is on the same side of the meridian as that indicated in Init. PA and 234.1 - 180 or 54.1 if the target is on a side of the meridian different from that indicated in Init. PA.  Of course, if you can not get a suitable guide star in the guider FOV, you will need to physically rotate your camera and then Initialize.  Initializing will of course give better guider calibration than conventional calibration.