This dialog is used to enter the coordinates on which the images to be measured are centered, to specify the speed and direction of the motion of the object to be traked, and the method used to stack the images. The software needs the coordinates so that the corresponding information can be extracted from the reference star catalogue, and that the images can be stacked, taking the motion of the object into account. The position entered here should match the actual coordinates of the image center at least to the precision specified for the Pointing in the program settings.

Object: If an object designation is specified, the software will search for a designation that starts with the characters you enter here in the MPCOrb databse. Note that, if you search for a numbered minor planet, you must include at least the leading parenthesis. For long-period and unnumbered short-period comets, you must include the 'C/' and 'P/', respectively. Blanks in the designation of the object are not significant, and there is no differentiation between lower- and uppercase letters. Alternatively, you may select the object using the object browser, which can be called by pressing the [...] button. When the cursor leaves the field (for example, after pressing the tab [Tab] key) the coordinates and motion calculated for the object will appear.

Right Ascension: Right Ascension, in Hours, Minutes and Seconds.

Declination: Declination in Degrees, Arc Minutes and Arc Seconds. Use the Radio Buttons to distinguish between northern and southern Declinations.

Object Motion: The speed (in Arc Seconds per Minute) and Direction (Position Angle) of the object. The Images will be stacked to follow that motion, so that the object appears fixed, while backround stars will appear trailed. The software will also display the mid-exposure time of the stacked image (UT): Use this time if you take the data for the object motion from an ephemeris. You may also use the object browser in this field by pressing the [...] button to select an object and set the motion (not the position) of that object. (This can be useful, for example, if you want to stack images with the motion of another minor planet or comet in the field.)

Stacking: The user can choose between three modes for stacking the images:

• Add: Sums up the pixel values from individual images. Before that, a pedestal is subtracted from the individual images to avoid saturation of pixel values.
• Average: Sets the pixel value of the final image to the mean of the individual images. The range of pixel values is therefore preserved, and pixels will not saturate when stacking images. For faint targets and/or images using only a small fraction of the dynamic range, pixel values in the stacked image might appear quantized.
• Median: This mode will almost completely remove stationary objects (like stars) when more than two images are combined (for two images, the 'Median' is identical to the 'Average'), and the object has moved more than the diameter of the stars on the images, which might be useful when tracking an object in crowded fields.

Related Topics:

• Center Position
• Object Browser
• Tutorial III