Although light travels 167,000 miles in a second, the distance of 61 Cygni (the only star whose distance is ascertained) is so inconceivably great, that its rays would require more than ten years to reach the earth. For stars beyond this, 20 — or even 1000 years — would be a moderate estimate. Thus, if they had been annihilated 20, or 1000 years ago, we might still see them to-day by the light which started from their surfaces 20 or 1000 years in the past time. That many which we see daily are really extinct, is not impossible — not even improbable
