NavList:

Hello Al

Welcome aboard. 

You can always measure the distance between any two stars.  We identify that as the "interstellar distance".  This angular displacement would be constant if we did not consider the affects of our atmosphere.  Our atmosphere causes refraction, which will change the interstellar distance in a small way.  The measurement is very useful for obtaining practice with your sextant (and in the long run, with calibrating the arc of your sextant).

{Before the purists jump all over me, I do understand that stars have proper motion, however, that is a detail not appropriate for this level of discussion}

For position finding, which is the essence of celestial navigation, the interstellar distance provides nearly zero information.  The near constant value is to be found anywhere on earth, assuming you can see the two stars.  Measure the distance in Australia or Africa, and when the effects of refraction are removed, the interstellar distance is identical.  So if we cannot tell what continent we are on, the interstellar distance won't do us very much good.

You may be thinking of the LUNAR distance, as the angular displacement between the edge of the swiftly moving moon and an ecliptic star can be used to determine longitude.  I will leave it to the lunatics (pun fully intended) to describe the lunar distance in greater detail.

The 'modern' practice of celestial navigation requires a horizon.  Measuring the altitude of the sun, moon, planets and stars above the horizon will yield several lines of position.  The lines of position are plotted and the intersection of those lines is indicative of your unique position on the globe.  But this cannot be described in a simple manner in one paragraph!   There is a lot of fun and interesting details to learn.

There are books that we can recommend to guide you.  You will find no greater resource for getting your questions answered than right here.

Brad