Percival Lowell's rehabilitation?

[Han Sibot]

Full moon: tonight I tried to experience the optical illusion of Venusian
spokes and Mars canals. Some time ago an article in Sky & Telescope
mentioned that Percival Lowell did his observations using a telescope with a
very small exit pupil (0.5 mm). Readers responded that Lowell might have
mistaken the shadow of his own retinal blood vessels and floaters for
spokes. So tonight I directed my old telescope at the moon, assuming it
appears like Venus or Mars through Lowell's telescope, and looked through a
0.5 mm pin hole into the eye piece. What a disappointment, I saw no blood
vessels, and my floaters were unimpressive. I am getting the impression that
the optical illusion is a hoax.

For comparison: without the telescope I was able to see retinal blood vessel
shadows using the same hole, by looking at a bright surface, but I had to
keep the pinhole moving rapidly around in front of my pupil, because as soon
as it stopped these shadows extinguished in a fraction of a second. In
addition, the blood vessel shadows gave me the impression that they follow
the motion of the eye, instead of belonging to the remote target. The just
don't behave like spokes on a planet.

Is there anyone who experienced in other curcumstances that this supposed
illusion is convincing?

[Orion]

As I recall, an important part of the illusion is superb seeing
conditions....both atmospheric transparency and steadiness...
Orion

"Han Sibot" <han...@freemail.nl> wrote in message
news:3e272ee3$0$141$8fcf...@news.wanadoo.nl...

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