Notes on Celestial Navigation
Celestial objects used for navigation
Navigation can be used to find out two coordinates.
- North Star, Polaris: easiest, best at determining latitude
- The Sun: need to know date for accurate coordinates
- Stars: need accurate coordinates
- The Moon: difficuly to use, fast moving, need accurate
coordinates (not covered here)
Polaris is abour 3/4 degrees from the North Celestial Pole (NCP).
It is easy to show that in the Northern latitudes, the altitude of the
NCP is equal to latitude and the the NCP lies along the north of the
One finds Polaris aligns within 3/4 degree of due North and that the
altitude of Polaris is within 3/4 of a degree of your latitude.
Refinements can be made with knowledge of the Local Sidereal Time.
The Sun is an obvious time-keeping tool. The hour angle of the
Sun can be used to measure time or longitude. It is the highest
altitude of the Sun that allows one to measure one's latitude. To use
the Sun requires a specific knowledge of its Right Ascension and
Declination. This is done by date:
Vernal Equinox: alpha = 0 hours, delta = 0 degrees
Summer Solstice: alpha = 6 hours, delta = +23.5 degrees
Autumnal Equinox: alpha = 12 hours, delta = 0 degrees
Winter Solstice: alpha = 18 hours, delta = -23.5 degrees
Coordinates for other dstes can be acquired from lecture slides, online
tables, or computer software.
These data are used in formulas such as those in the next section
(Stars) or Lecture 7 (Time).
Latitude can be determined using the declination and the highest
altitude of the Sun. One might have to extrapolate the path to
the meridian crossing.
zm = zenith angle at meridian crossing (negative if to the south, positive if to the north), delta = declination, l = latitude (south denoted
by negative values)
zm = delta - l
Formulas for time and longitude are covered in other notes
One needs up to date celestial coordinates and basic knowledge of
phases to use the Moon. This proves the most difficult data to