Celestial Navigation I Calculating Latitude By Observing Heavenly Bodies

Geographical Position (GP) Imaging a line linking a heavenly body and the center of the earth The point where this line cuts through the earth is the body’s Geographical Position (GP)

A person who stands at the GP of a body would look straight up to see that body. If you are not at the GP when you look up you only see your own zenith, and not the body in question To you the body is at a different elevation in the sky. The angle between the body and your own zenith is the zenith distance

Altitude & Declination The declination of a heavenly body is simply the latitude of its GP. This information is available to Navigators in published logs. DEC E P Ad Astra → You are HERE You are at a point due North of the GP. To see the star you look to the SOUTH The horizon line is a tangent to the earth that passes through your position The altitude is the angle of elevation you measure for the star above the horizon Z GP ALT

Altitude & Declination Ad Astra → E PZ We must also consider the fact that the tilt of the Earth changes seasonally as the Earth orbits the sun…… The GP (and so the declination) of a star thus changes throughout the year. It is important that any navigator has up to date charts that give declinations on a daily basis. GP