There are found in the sky many thousands of these close double stars, of which some are only optically double-i.
"A Text-Book of Astronomy"
George C. Comstock
For up to that time it had been supposed that such grouping in occasional pairs or triplets was chance coincidence, the two being optically foreshortened together, but having no real connection or proximity.
"Pioneers of Science"
Oliver Lodge
The paths do not appear to us to be parallel, because of perspective: they seem to radiate and spread in all directions from a fixed centre like spokes, but all these diverging streaks are really parallel lines optically foreshortened by different amounts so as to produce the radiant impression.
"Pioneers of Science"
Oliver Lodge