How far back in time can the naked eye see?

"Whenever you observe an object, you aren't viewing it in its present state. Instead, we're held back while light travels through space. Visible artificial satellites appear as they were ~1-2 milliseconds ago. The farthest naked eye Solar System object, Uranus, is 2 hours and 40 minutes in the past. The closest stars, in Alpha Centauri's system, are ~4.3 light-years away; there, it's early 2016 on Earth. The second brightest star, Canopus, sees a pre- Industrial Revolution Earth: 310 light-years distant."

"Deneb, anchoring the Summer Triangle, appears as it did 2615 years ago; Athenian Democracy hasn't yet arrived. Eta Carinae, 7,500 light-years away, witnesses the Black Sea's flooding. The oldest naked-eye starlight arrives from V762 Cassiopeiae, 16,300 years old: when humans first entered North America. Numerous visible globular star clusters are farther, with Messier 3 the most distant. It's 33,900 light-years away, corresponding to the final demise of Earth's Neanderthals."

"It's 33,900 light-years away, corresponding to the final demise of Earth's Neanderthals. Galaxies outdistance all other visible objects. The Triangulum galaxy even bests Andromeda: 2.73 million light-years away, predating Homo Habilis. Only temporary, transient events are farther. Gamma-ray burst GRB 080319B was visible for ~30 seconds on March 19, 2008. 7.5 billion light-years away, its light predates Earth's existence by ~3 billion years."

Light from astronomical objects takes measurable time to reach observers, so observed appearances are historical. Artificial satellites appear as they were ~1–2 milliseconds ago, while Uranus appears about 2 hours and 40 minutes in the past. Alpha Centauri shows Earth as of ~4.3 years earlier; Canopus views a pre-Industrial-Revolution Earth from 310 light-years away. Deneb's light is 2,615 years old, Eta Carinae's is 7,500 years old, and V762 Cassiopeiae's light is 16,300 years old. Messier 3 at 33,900 light-years corresponds to Neanderthal final demise. Triangulum at 2.73 million light-years predates early Homo, and GRB 080319B arrived from 7.5 billion light-years.

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