Now the speed with which this vibration passes is so
great--about 186,000 miles in a second--that when we are considering any
object in our own world we may regard it as practically instantaneous.
When, however, we come to deal with interplanetary distances we have to
take the speed of light into consideration, for an appreciable period is
occupied in traversing these vast spaces. For example, it takes eight
minutes and a quarter for light to travel to us from the sun, so that when
we look at the solar orb we see it by means of a ray of light which left
it more than eight minutes ago. From this follows a very curious result.
The ray of light by which we see the sun can obviously report to us only
the state of affairs' which existed in that luminary when it started on
its journey, and would not be in the least affected by anything that
happened after it left; so that we really see the sun not as it is, but as
it was eight minutes ago. That is to say that if anything important took
place in the sun--the formation of a new sun-spot, for instance--an
astronomer who was watching the orb through his telescope at the time
would be unaware of the incident while it was happening, since the ray of
light bearing the news would not reach him until more than eight minutes
later.
Pages:
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203