Star-Sighting
Star-sighting generally refers to a type of navigation which uses the position of the stars to determine direction or the observer's position. Polaris, (the Pole Star) can be used to determine North at any time of night when stars are visible in the Northern Hemisphere. Other stars can be used for navigation if the time is known. An almanac may enable directions or positioning using numerous stars or planets.
Although star-sighting is often thought of as out of date with today's GPS systems, star-sighting still plays a critical role in the guidance of some ballistic missiles, especially ICBMs. Since the elliptical trajectory of ballistic missiles essentially enters them into sub-orbital spaceflight (with altitudes up to 1200 km), star sighting is used to correct inertial navigation system errors and determine the location of their target.[citation needed]
