Robert McNaught wrote: >>Also in theory, an orbit can be deduced from two positional >>observations at two different times. This method generates two >>possible orbits that pass through the two points. One of the two >>orbits is obviously "wrong" and is discarded. > >Actually, there are an infinite number of orbits that pass thru two >points/times. My error :( In the two-position and time-of-flight problem, I overlooked that the position vectors are just that, vectors. Obviously the distance or length component is unknown when making an alt/az or RA/dec observation. Don't we all have radars in our back yards? :) -- Jim ------------------------------------------------------------------------------ Jim Varney | 121^ 23' 54" W, 38^ 27' 28" N | Sacramento, CA Member, SeeSat-L| Elev. 31 ft. |jvarney@mail2.quiknet.com ------------------------------------------------------------------------------