When we look outward into space, we’re looking backwards in time. That’s because light moves, at the speed of light. It takes time for the light to reach us.
But it gets even stranger than that. Light can be absorbed, reflected, and re-emitted by gas and dust, giving us a second look.
They’re called light echoes, and allow astronomers another way to understand the Universe around us.
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References:
https://www.nasa.gov/feature/jpl/arecibo-radar-returns-with-asteroid-phaethon-images
https://www.nasa.gov/mission_pages/LRO/multimedia/lroimages/lroc-20100413-apollo15-LRRR.html
https://www.spacetelescope.org/videos/heic0617a/
https://www.nasa.gov/feature/jpl/light-echoes-give-clues-to-protoplanetary-disk
https://www.nasa.gov/feature/goddard/2019/nasa-s-nicer-mission-maps-light-echoes-of-new-black-hole
https://hubblesite.org/contents/news-releases/2017/news-2017-42.html
https://www.eso.org/public/images/potw1814a/