And since we know (among other things) the exact speed of light in our atmosphere, we can calculate how distant the plane is. (techcrunch.com)
Although the measured speed of light has decreased only about 1 % during the past three centuries, the decrease is statistically significant, because measurement techniques can detect changes thousands of times smaller. (creationscience.com)
The finite speed of light means that the further away a cosmic object is, the longer its light takes to reach us. (newscientist.com)