Tutorial III - Advanced (using three stacked images and FITs file information)


Task: Identify the image files involved where a moving object passes close to ANY field star so those images can be rejected in further processing


Materials required:


- A set of individual images of a moving object, used to generate the following three stacks:


Stack A - a stack of some or all of the available images, combined using the object's motion that allow the object to be seen (even though it may be partially obscured by star trails)

Stack B - a stack of the first and last image only, combined using the object's motion, to accurately determine the full extent of the object's motion.

Stack C - a stack of at least the first three, preferably the first 10+ images, stacked with ZERO motion, to reveal all the field stars and galaxies.


Note: This tutorial gives instructions using Astrometrica to blink these three stacks. If using other software, equivalent functionality will be required.


Steps:


  1. Follow Tutorial II to Step 7 (Show object path against star background)
  2. Drag and drop FITS files on the Screen Ruler Control window
  3. Deselect the files to be rejected
  4. Copy just the selected files to a folder for stacking
  5. Result - Stack the files copied to the Stacking folder


Step 1.         Follow Tutorial II to Step 7 (Show object path against star background)


Follow Tutorial II to step 7 where the enhanced star background (from combining a number of images with zero motion) is overlaid with the Screen Ruler line, now accurately indicating the track of the moving object from the first to the last available image.



Step 2.         Drag and drop FITS files on to Screen Ruler Control window


In Windows Explorer select all the FITS files and use the mouse to drag and drop them on the FITS files area of the Control window:



When the files are dropped the Screen Ruler window changes to show blocks of alternating colour representing the start and end exposure time for each image. The Screen Ruler Control window area where the FITs files were dropped shows a list of the files and by default they are all selected. 



Step 3. Deselect the files to be rejected


Initially all files are selected. Selected files appear with alternating colours, in the example above using red and aqua. Files can be deselected by either using the list of files in the Control window, or by holding the Ctrl key while dragging the mouse on the Screen Ruler window. The Control window list follows standard Windows conventions on selection (e.g. click on a line to select one line and deselect all others, press Ctrl+A to select all, hold Ctrl while clicking on a file to change the selected status of just that line etc.).


In the example here deselected files are shown dimmed and not coloured. Deselected files can be reselected by either using the list of files in the Control window, or by holding the Shift+Ctrl keys while dragging the mouse on the Screen Ruler window.


Now, use the mouse to deselect files where the object passes close to field stars by holding the Ctrl key and dragging the mouse along the appropriate parts of the Screen Ruler window. The files selected in the Control window are automatically updated:



If files need to be reselected, either use the list on the Control window, or hold Shift+Ctrl while dragging the mouse, or place the mouse on a file location and press the F7 function key to toggle the selection of individual files on or off.


Note that when the mouse is moved along the ruler the tooltip now reads out the FITs file name as well as the image sequence number.


Step 4.         Copy just the selected files to a folder for stacking


Rather than manually noting the image numbers needing to be rejected, and then manually selecting just the required images in Astrometrica, the Screen Ruler can copy the selected files from a source folder to a destination "stacking" folder where the required image files can be conveniently selected for the final stacking process.


The source and stacking folders are configured in the Settings window with the FITSSourceFolder and FITSStackingFolder settings, but can also be quickly set by dragging from Windows Explorer either the respective folder, or a FITS file in the folder to the equivalent toolstrip button in the Control window, for the source folder or for the stacking folder. Here the source folder is being set, but the stacking folder can be set in the same way:



When the FITSSourceFolder and FITSStackingFolder settings contain valid folder names, press the Open Source Folder and Open Stacking Folder buttons to open those folders using Windows Explorer. Only when both settings are valid and refer to different folders will the Copy selected files button then be available.



To check the folder names are correct before pressing the Copy selected files button, hover the mouse over the button, the action to be performed by the button will be displayed, for example:



Step 5. Result - Stack the files copied to the Stacking folder


Stacking the files selected and copied into the stacking folder in step 4, i.e. files 1-9, 13-22, 27-33, 36-37 and 46-48 produces this result, with the moving object completely separated from all the background star trails. Astrometry and photometry can now be confidently measured from the stacked image:


Tutorial III

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