The Sun you are looking at is the Sun of 8 minutes and 20 seconds ago; were it to go out this instant, the sky would stay bright for exactly that long. The Moon runs 1.28 seconds late, Mars from 3 to 22 minutes depending on orbital position, Proxima Centauri 4.25 years, and Andromeda sends us a picture of 2.5 million years ago. A telescope is therefore a one-way time machine, and the farthest it reaches is ancient background light that has been travelling for 13.8 billion years.
The Sun you are looking at is the Sun of 8 minutes and 20 seconds ago; were it to go out this instant, the sky would stay bright for exactly that long. The Moon runs 1.28 seconds late, Mars from 3 to 22 minutes depending on orbital position, Proxima Centauri 4.25 years, and Andromeda sends us a picture of 2.5 million years ago. A telescope is therefore a one-way time machine, and the farthest it reaches is ancient background light that has been travelling for 13.8 billion years.
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