C2A has a simple tool which lets you point a telescope to a position on the sky such that at a given time a specified object will be at the centre of the telescope field. This ability is called “pre-pointing” and it is particularly useful in the observation of occultations where, several minutes or several hours before the event, the telescope is set in position with tracking stopped in anticipation of the event. Imaging is started some minutes before the expected occultation and the target star drifts into the stationary field. You can also start tracking at the exact time of the event and the target object will be at the centre of your field.
C2A traces a line on the field with position targets which show where the telescope should be pointing at the different times. The pre-pointing tool is called by using the Prepoint track… command in the Telescope menu. Shift+F9 is a shortcut for this command. It has the following format:
A pre-pointing line is displayed on the basis of the following fields:
The option Display all minute marks on line lets you force the display of minutes on the pre-pointing line regardless of the zoom level. If this is not checked, C2A automatically determines the scale of minutes in relation to the zoom level.
The option Display target tat current time lets you display a target on the pre-pointing line that shows where we are at the current time of the map. This target facilitates the job of pointing the telescope during the preparation phase.
Time labels on the map are displayed in UT or local time, which depends on whether the option Display local time rather than UT is checked on the Date tab of the Options dialogue box.
The screenshot below shows typically what you get when you plot a pre-pointing line for an occultation observation:
At 00.08, which is about 8 minutes before the event, the telescope must be pointing at the position indicated by the target with the tracking stopped. The target star will then move over the minutes until arriving at the centre of the field at the chosen time.
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