It is said in the literature, I believe, one needs several nights of observations to calculate an orbit for, say,an asteroid. Using celestial mechanics mathematics and methodology, one produces the six orbital elements. It seems to me that most introductory texts on the subject, talk about Keplerian Laws, and the geometry of an orbit. Physics too, but how do observations fit into all this to finally produce the "orbit". An observer is only reporting time and position (RA, Dec), so how do distances figure into this? An observer cannot provide them. Do they fall out of the methodology I refer to above?