Transcript Celestial Navigation I

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)
Geographical Position (GP)
If you are not at the GP
when you look up you
only see your own
To you the body is at a different elevation
zenith, and not
in the sky. The angle between the body and
the body in
your own zenith is the zenith distance
question
A person who stands at
the GP of a body would look
straight up to see that body.
Altitude & Declination
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
Z
You are
HERE
P
The altitude is the angle of elevation you
measure for the star above the horizon
ALT
GP
DEC
E
The declination of a heavenly body is simply
the latitude of its GP. This information is
available to Navigators in published logs.
Altitude & Declination
We must also consider the fact that the
tilt of the Earth changes seasonally as
the Earth orbits the sun……
P
Z
GP
E
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.