Global Positioning System Reference
In-Depth Information
FIGURE 7.10.
Celestial navigation by the altitude intercept method. (a) Light from a
navigation star arrives at the earth's surface at angle
a
, as measured by an observer.
If we know the star's position in the sky, then we know that the observer must be
somewhere on the circle shown. (b) A second star observation yields a second circle;
the observer is at one of the two intersection points. A third circle would yield an
unambiguous location for the observer, but usually, as here, the third circle is hardly
necessary.
