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Star "trail" for pre-pointing

I am member of the International Occultation Timing Association (IOTA). We regularly observe asteroid occultations using a technique we refer to as "pre-pointing". With pre-pointing, we point the telescope to the point in the sky where a star will pass over at a specified LATER time during which the star will be occulted by an asteroid. Many years ago, Bill Gray added a "star trail" feature to his program, Guide, which allows us to generate charts showing where and when we should point the scope in advance to see a specific star pass over the "target location" at the specific time of the occultation. I already use SkySafari in the field for occultations and It would be very handy to have the star trails in the field using SkySafari (so I don't have to go back/forth with printed charts from Guide). Please contact me if this is a possibility and you would like more details/input on the useage of this feature. Thank you for your consideration of this request.

For further information, here is a link to a powerpoint presentation describing how we use pre-pointing:



  • 0
    Bill Tschumy


    I assume these must not be tracking scopes?  Otherwise, why not just point the scope to the star that is going to be occulted.

    Your request is pretty specialized and no one else has ever asked for it.  As such it would have to be a low priority item.

    Since you know the time the occultation occurs, why can't you advance time to that time and see where the star is (Alt/Az)?  That would seem to do the same thing as star trails.

  • 0
    Steve Preston

    Hi Bill,

    Yes, we primarily use pre-pointing for simple setups with no tracking.  Although pre-point can also be useful for tracking scopes when you are aiming for a dim star or when you would rather not stay up for hours just to make sure the star doesn't drift out of the field of view.  We have a program that generates a list of stars along with the pre-point times and offset from the declination of the "target star".  However, a chart with the track can be a big time-saver.  Some members of our group will setup as many as ten stations (scopes) in several hours prior to the event.  When setting up several stations, it is hard to predict exactly which pre-point star you will need as you are setting up a station.  The charts provide some flexibility in choosing a star and allow some chance of recovery if (when) you hit a snag along the way.


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