To measure their orbit, which tells you how close they'll come, all you need to see is a point of light over a period of several nights. To measure their size you need to either see a visible disk or know how light or dark the object is. If it's light colored it could be reflecting up to about 40% of the light that hits it. If it's dark it could be reflecting less than 10% of the light that hits it and could be huge and still look small and dim.
It is similar to seeing an aircraft’s lights at night off in the distance. Can you tell the wingspan of the aircraft ?
And if its conductive it could be “reflecting” 300% of the light hitting it like a giant arc lamp.