Visualising a small ****** map of Comet 2P/Encke:
Enter "Encke" (1000025) as a moving single target using the HSpot Target entry window (the bull's-eye icon).
From the Images menu, select "ISSA image". Make sure that Encke is the target in the ISSA image dialogue window. Accept the defaults (e.g., 5-degree image size) and press OK. Enter *****2006 Aug 12 00:00:00**** as your selected date; this is not the default, but the midpoint of the first visibility window in 2006. You can select this by clicking on the date range for that window.
Resize the HSpot window to fill the screen and use the magnifying glass with the red "plus sign" (upper left) to zoom the image.
Go to the Encke icons on the right and bring up the ephemeris window by clicking on the list icon . Click "Show All Dates". Note that Encke takes a little over two months to cross this 5-degree ISSA image. But how far is it travelling?
Select the Distance Tool from the Overlays menu. Using the left mouse button, click at one date on the trajectory, e.g., *****2006 Jul 22, and drag approximately to the next shown date to the left, ****2006 July 25. Click on the Encke check mark to toggle off the trajectory and dates, so that you can read the distance off the display. The distance value can also be read by clicking on the Distance overlay table icon.
Click the Encke trajectory back on and the distances line off. Go into the Encke list icon and "Hide all dates," or select just a few for display.
Click on the IRAC AOT icon at the top of the main HSpot window. Check that Encke is the target. Select Frame Time = 100 seconds, Mapping Mode "yes", and OK for the default in the mapping window. Click OK at the bottom of the AOR window.
In the Overlays Menu, select AORs on Current Image. Answer Yes to using the same visibility date. HSpot should now display the **** aperture positions on the sky for this ***x*** map (see Figure 19.10, “***x*** SPIRE/PACS Map”).
Click on the SPIRE/PACS/HIFI display layer control pointings icon. Select “Animation w/Trail”. Note that the mapping path that SPIRE/PACS may generally take is a zigzag shape on the sky, as compared to the ****x**** square that would be expected for a fixed target. This is because the spacecraft tracking of the rapidly moving Encke is being superimposed on the mapping motions of the SPIRE/PACS/HIFI map. The Herschel pipeline has the capability to take these frames and recreate the map of the target in the target's rest frame. This will be a rectilinear map with the tracked extended target reassembled as a continuous image, but with the disjointed pieces of sky background that you may see.
