NightCal is a tool for basic observation session planning. It produces a single A4 sheet monthly calendar telling the user when it gets dark, when the Moon rises and sets and what the Moon should look like when it does make an appearance. It also provides data on the elongation of the inferior planets and quick aide memories for planetary conjunctions. The output is designed to be printed so that you can stick it on your notice board at home or at work or saved as a graphics file for inclusion in newsletters or publishing on the Web. There is a known problem with installing Nightcal on Vista and later versions of XP. When installing NightCal on the Microsoft Vista and later versions of XP Pro NightCal will appear to install perfectly. However, for some bizarre reason known only to Microsoft, Vista and later versions of XP Pro sometimes then move the executable file (Nightcal.exe) and other associate files from the Nightcal folder to the user's document folder. Don't ask me why. Because Nightcal is a standalone executable it should still run, but the desktop shortcut will now be pointing to the wrong folder. There are two ways to fix this: 1. Re-instate the desktop icon, deleting the original shortcut then replace it with a new shortcut to the new location of NightCal. 2. Manually move the relevant files back into the NightCal folder, where they should now stay.