The principles of celestial navigation are simple. The harder mathematics
come in details of calculations, and a computer program like ASNAv
will take care of this for you, so don't be afraid to read this page. It's pleasant
to understand how it is possible to find his position on Earth just be looking
at a few stars… The celestial mechanics is precision mechanics. It is possible to calculate
the exact position of a heavenly body (star, planet, moon, sun) in the sky at
any given time. Knowing the position of the star in the sky, the measure of
the angle between the horizon of the observer and the star, using a sextant,
is enough to determine the observer position in latitude and longitude (in fact,
we will see that at least two measures are needed).


Let's show this by the example of another situation at sea: imagine you observe
a lighthouse from a certain distance. With the sextant, you measure the angle
alpha corresponding to the height of the lighthouse
seen from your position.
If you know the height h, you can find your distance d
from the lighthouse. On a chart, you can draw a circle centred on the lighthouse
with a radius d. You are somewhere on the
circle. This is your circle of position.
