A handheld electronic apparatus includes a positioning module, a sensing module, a constellation database, and a processing module. The positioning module generates location information associated with the handheld electronic apparatus according to a satellite signal received by the handheld electronic apparatus. The sensing module detects a vertical tilted angle and a horizontal observing direction associated with a positioned state of the handheld electronic apparatus. The processing module retrieves corresponding real-time constellation information from constellation data stored in the constellation database according to timing information, the location information, the vertical tilted angle, and the horizontal observing direction.