Posted 04 August 2011 - 08:05 AM

A much simpler way:1. Get the latest Stellarium, 0.11.0 (version 0.10.6 will also do, but its bookmarks are out of date because the MPC changed their website)2. Enable the Solar System editor plug-in if it hasn't been enabled:2.1. Open the "Configruation window" and go to "Plugins";2.2. Select "Solar System Editor" in the left column (the plug-in's description should appear);2.3. If the "load at startup" box is not checked, check it and restart Stellarium.3. Go to the same plug-in screen, select the same plug-in and click on the "configure" button.4. In the window that opens, go to the "Solar System" tab, then click on the "Import elements in MPC format window".5. In the window that opens, select "Comets", then "Download a list of objects from the internet".5.1. If you are using 0.10.6, copy this URL to the "URL" box: http://www.minorplan...s/Soft00Cmt.txt 5.2. If you are using 0.11.0, just select "MPC's list of observable comets" from the bookmarks list.6. Click the "Get orbital elements" button and wait for the file to be downloaded.7. After it has finished downloading, it should display a list of comets. Find "C/2009 P1 (Garradd)" in the list, check the checkbox in front of it and click the "Add objects" button.An advantage of this method is that it pulls absolute magnitude/slope parameter data along with the orbital elements, which allows better magnitude estimation that playing hit-and-miss with the diameter.