What if the sun disappeared?
If the sun disappeared, for eight-and-a-half minutes we’d have no idea that the sun had gone. We’d still see it – lingering, like a ghost – in the sky above Earth’s day side. As soon as the last of the sun’s light reached us – eight-and-a-half minutes after the sun itself disappeared – the sun would blink out and night would fall over the entire Earth.
Not until that instant would Earth sail off in a straight line into space. Einstein’s special theory of relativity tells us that no signal in the universe – not even the tug of gravity – can travel faster than the speed of light – about 300,000 kilometers, or 186,000 miles, per second. Though free from the sun’s gravity, we’d be traveling at the same speed as before – about 18 miles, or 30 kilometers per second. So Earth would be traveling at the same speed as always into eternal night.
If you were on Earth’s night side when the sun disappeared, you might not notice anything … at first. But then the night sky would begin to change. For example, if there were a full moon – which shines with reflected sunlight – its light would disappear a few seconds after the sun’s light blinked out. Over the course of several hours, the planets would wink out one by one, as they reflected the last of the sun’s light to us.