MediumScience
I shine brightest in the dark. I have burned for billions of years yet you can cover me with your thumb. I am enormously far away yet I guide sailors home. What am I?
Answer: A Mirror. Light takes a tiny but real amount of time to travel from you to the mirror and back to your eyes. So the reflection you see is technically from the past — however infinitesimally small that gap is. A beautifully precise riddle.