Spot Something On A Distant Planet? It Might Be Much Closer Than That
In the 1890s, Percival Lowell saw some markings on Mars that looked a whole lot like canals. For years, people thought about this finding and wondered if it meant evidence of intelligent life out there, or some kind of life at least. Unfortunately, while images of Mars might seem to show canals, these vanish when you look at a higher resolution.
Lowell also figured out the best place to build observatories and made progress toward finding Pluto, so he wasn't a total nut. But he also did make one other nutty finding, and this was one that no one else was able to replicate. He pointed his telescope toward Venus and saw what he called spokes, extending outward from a dark central spot. They looked the same no matter where Venus faced, which raised some interesting ideas about the planet's orbit.
No one else managed to see those spokes. Nor did we see any sign of them when we sent actual probes to the planet.
We think we now know what Lowell was actually seeing, and it was a lot closer to him than the surface of Venus. No, not something floating in Earth's atmosphere—think closer than that. And no, it wasn't a smudge on his telescope's lens—think closer than that.
Likely, Lowell was seeing the blood vessels in his own eye. When you shrink the aperture of a telescope really small, as Lowell liked to do, light hits your cornea at an angle you're not used to. This light now casts shadows of your own eyes' blood vessels onto your retina. Here's the unsettling side of this, though: Those vessels are always there and always visible to you whether the light's at a weird angle or not. It's just that most of the time, your brain is so used to the way those thingies look, that you've learned to ignore them.
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Top image: NASA