True bearing to a star

The true bearing toward a star’s projection point can be calculated from the azimuth. If the azimuth is from north toward west (N azimuth W), then true bearing = 360° - azimuth. If the azimuth is from north toward east (N azimuth E), it is the same as the true bearing.

Another way to say the same is that if you are in the Northern Hemisphere and the local hour angle is less than 180°, the azimuth is western and true bearing = 360° - azimuth. If the local hour angle is greater than 180°, the azimuth is eastern and true bearing = azimuth.

If you are in the Southern Hemisphere and the azimuth is expressed relative to true south, the rules are as follows:

If the azimuth is toward the east (S azimuth E), i.e. the local hour angle (LHA) is greater than 180°, then true bearing = 180° - azimuth.

If the azimuth is toward the west (S azimuth W), i.e. the local hour angle (LHA) is less than 180°, then true bearing = 180° + azimuth.

C o n t e n t s

• Position fixing from the stars
• Night sky
• Celestial sphere
• What you see from the North Pole as the Earth rotates
• How the night sky changes when you travel to the equator
• Effect of Earth’s rotation on the night sky at the equator
• Celestial meridian, upper and lower culmination
• Change in star altitude at the North Pole, equator, and in between
• Declination
• Example of determining latitude
• Hour angle, Greenwich Hour Angle (GHA)
• Aries, Greenwich of the celestial sphere
• Sidereal hour angle (SHA)
• Local hour angle (LHA)
• Relation between hour angle and time
• Example of determining longitude and latitude from the Sun at noon
• Relation between angles, degrees, and nautical miles on Earth
• Position circle
• Azimuth (A, Azimuth)
• True bearing to a star
• Nautical triangle
• Solving the nautical triangle (sight reduction)
• Position fixing from stars using Marcq Saint-Hilaire’s intercept method
• Star identification
• Details and practice
• Time
• Time difference (ΔT)
• Altitude measurement
• Example of position fixing
• Twilight
• Calculating twilight time
• Navigation Association exam