Starry Night looks for a file called Comets.txt when it starts up and, if found, will load the positions of the first 100 comets found in this file. Since the orbital elements of comets are constantly changing it is a good idea to update this Comets.txt file from time to time. The Comets.txt file contains positions of comets calculated by the Planetary Services Division of the Smithsonian Astronomical Observatory in Cambridge, Massachusetts.
To update Starry Night\'s comet data: open the Comets.txt file in your web browser by clicking the Comets.txt link above. Select "Save As..." from your browser\'s File menu and replace the Comets.txt file in Sky Data folder. Be sure to save the file as "text" and make sure the C in Comets.txt is a capital letter C.
If you are tracking a specific comet that you want to add to Starry Night try using the Orbit Editor. The Orbit Editor is a good tool for learning about celestial mechanics. Celestial mechanics is usually passed over in introductory Astronomy courses, because the mathematics and time needed to grasp orbital concepts is just too involved for most students. Starry Night provides an interactive simulator where the orbital elements of an object can be changed in a visual manner making a complex subject understandable and, dare we say it, fun.
For more information about adding a new planet, asteroid, satellite, moon, or comet to Starry Night see "Using the Orbit Editor".
See also: Guide to adding comets by writing data directly to the comet.txt file
And finally I understood what to do and it worked. So now I have my comets. Thanks a lot for supporting