Astronomers locate objects in the sky using a set of coordinates called declination and right ascension that are the analogous of latitude and longitude on the Earth. Right ascension is measured in hours, minutes and seconds with one hour being equal to 15-degrees. The sidereal time is the right ascension of the point that is on the zenith at any given time. Astronomers use sidereal time to know the orientation of the sky above them and to set their telescopes accordingly.
Sidereal is the PalmOS application that displays sidereal time. It will also display local time, UTC and the modified julian date. On a color device, you can set the display to red-on-black to preserve your night vision. | 
