Thousand-year-old Light
But we have a much more striking illustration and correspondence in the
case of the transmission of light from the distant stars, which we will
do well to carefully consider. Light travels at the rate of 186,000
miles per second. A "light-year," as known to astronomers, means the
distance traversed by a light wave (at the stated rate of travel) during
the period of one of our earth years. Some of the distant stars are
stimated to be fully one thousand light-years distant from us; or, in
other words, the light we now perceive as coming from them really is the
light that left them one thousand years ago. If one of these stars were
to be destroyed, observers on this earth would not become aware of it
for a thousand years. The star whose light we may now perceive may
actually have been destroyed nearly one thousand years ago. Other stars
are only one hundred light-years removed from us in space; others only a
few years; others only a few hours. But the principle is just the same
in all cases, namely, that we see the stars not as they are at the
present moment, but as they were when the light left them, perhaps many
years ago. Thus, as you see, we may actually perceive events long after
their happening.