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Author Topic:   Science Questions
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Message 1 of 10 (833158)
05-18-2018 2:18 AM

I thought that there was a topic for asking questions without starting a discussion, but I couldn't find it (plus I'm on my laptop on vacation). If a moderator knows of a more proper topic to place these questions in, do please make the necessary corrections.

1. Walking along yet another medieval wall, this time in Porto Venere, I noticed the variety of rocks used to build that wall.

Question: Is or was one first step of a geologist setting out to study the geology of an area to visit such old constructions in order to see what the previous generations had found around there?

2. Physics question. There's a rotating exhaust vent which is very shiny, highly reflective. At night it seems to have a prismatic effect as it takes yellow and white street light light and generates a rainbow of colors -- mainly we see glints of red and blue along with white. Is there an explanation for that effect?

Replies to this message:
 Message 3 by Modulous, posted 05-18-2018 10:40 AM dwise1 has not yet responded
 Message 7 by Taq, posted 05-18-2018 4:19 PM dwise1 has not yet responded

Posts: 4480
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Message 8 of 10 (833242)
05-18-2018 4:27 PM

The Prismatic Exhaust Thingee
Actually, these things appear to be very common in this neck of Liguria. Our own Air-BnB has one. A few points/observations:

  • The surfaces are smooth and very shiny. No evidence of any kind of grooves on the surface -- the only thing I notice on ours is some blotchy smudging by deposits from whatever's in the rain drops that have hit it over time.

  • This happens night after night through different weather conditions, so that should rule out jar's condensation droplets.

    However, I would like to describe a visual experience one rainy day on the 405. It had just rained and there was enough rain on the road surface that the cars' tires kicked up a lot of water spray. The sun was finally breaking through behind me, creating the rainbow effect on that water spray. Poetically, it looked like all the cars in front of me were riding on clouds of rainbows. Very beautiful to see.

  • It is the wind that's spinning those exhaust vents. The effect is in effect all night long -- maybe it's happening in the daytime too, but we cannot see it then. Also, the running of heat or A/C is apparently very strictly controlled and restricted in Italy and now is not the time of year that you would get either. I have no clue what could possibly be getting vented up that exhaust, but nothing could possibly be running all night long, night after night.

An additional factor is that there's a bright white artificial light source farther up the hill which I hadn't noticed last night and which is more likely the source of the light being refracted/whatever.

This exhaust thingee is smaller than ours and seems to spin more readily and more rapidly. I thought that the spinning may be a factor, but it's hard to imagine that such a relatively low spin rate could produce such results. It's fun to watch. At first, I even thought it was some kind of device to scare off the seagulls who nest atop so many of these roofs -- our own place is called "Seagulls' Nest" -- but since that roof has a nest with gullettes (just what do you call infantile gulls?) then that can't be working.

Anyway, you're all smarter than I am, so what's the story?


Angles and dangles. They're always important with rainbow effects. Angles and dangles.

The exhaust thingee is slightly towards my right, maybe 10 to 30 degrees. The white light source is maybe 100 degrees to my right. The light source is elevated maybe 10 to 20 degrees above my eyelevel, which the exhaust thingee is depressed maybe 10 degrees below my eyelevel.

Edited by dwise1, : ABE

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 Message 9 by Taq, posted 05-18-2018 5:03 PM dwise1 has responded

Posts: 4480
Joined: 05-02-2006
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Message 10 of 10 (833270)
05-19-2018 2:03 AM
Reply to: Message 9 by Taq
05-18-2018 5:03 PM

Re: The Prismatic Exhaust Thingee
I think it has to do with the "refresh rate" of the photosensitive chemicals in your eyes.

Would that also show up in a video I took of it?

Lots of white flashes, some red, lesser amount of blue.

The parallel edges might have some bearing after all. The object is roughly spherical, though a bit wider at the bottom than at the top. It's constructed of strips of metal which are turned out at an angle, maybe 10 degrees or less. It's size is maybe 4 to 6 inches in diameter. The metal surface is smooth and highly polished, making it very reflective.

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