So if any star that you are observing from Earth is 100 light-years away then what you are watching from your telescope is not its current status but what the star was 100 years ago. This is also why sometimes telescope is called an. Measuring astronomical distances in miles or kilometers is impractical because of the huge distances and the scale of figures being used. Measuring in light years also allows astronomers to look back in time.
Empedocles thought that light traveled and so must have a rate of travel. Aristotle, in contrast, argued that light was instantaneous.Galileo Galilei conducted experiments on the speed of light using people placed on hills around a mile apart, holding lanterns. In 1879, physicist Albert A. Michelson used mirrors and lenses to measure the speed of light at 186,355 miles per second . Forty years later, he used a mile-long depressurized tube of corrugated steel pipe to simulate a near-vacuum and give a better measurement, which was only slightly lower than the accepted value of the speed of light today.
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