Astronomical Events
A few examples of what you can ask Wolfram|Alpha about:
compute the date and properties of an eclipse
get the next eclipse occurring after a given date
specify a point from which an eclipse should be visible
get information about a meteor shower
do computations with meteor shower properties
Sunrise & Sunset
compute sunrise/sunset times
compute sunrise/sunset times for a specified date
Solstices & Equinoxes
compute dates of solstices and equinoxes
get information about lunar phases
find out when a phase will occur
find the moon's phase on a particular date