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TampaDude
2009-Apr-11, 04:52 PM
Last night, I was looking at the moon with my naked eyes, with a broken layer of clouds drifting by from right to left at a fairly good clip, when I experienced something strange, something that I don't recall experiencing before in all my many years of observing.

The whole layer of clouds would frequently appear to "jump" or "jerk" up and down and sometimes backwards as I watched them. I know this had to be an optical illusion, because it would be impossible for the clouds to make such motions in reality. Did I experience something like the autokinetic effect? Has anyone else here experienced the same thing as I described it?

TomBurgessinspace,09
2009-Apr-11, 06:14 PM
Like i said above Last night, I was looking at the moon with my naked eyes, with a broken layer of clouds drifting by from right to left at a fairly good clip, when I experienced something strange, something that I don't recall experiencing before in all my many years of observing.

The whole layer of clouds would frequently appear to "jump" or "jerk" up and down and sometimes backwards as I watched them. I know this had to be an optical illusion, because it would be impossible for the clouds to make such motions in reality. Did I experience something like the autokinetic effect? Has anyone else here experienced the same thing as I described it?
Hope this aint a double post dudez

TampaDude
2009-Apr-12, 01:10 AM
Uh, TomBurgessinspace,09...I was looking for an educated answer, not the parroting of what I already posted...thanks. :hand:

Chilinuttz
2009-Apr-12, 06:50 AM
My suggestion is that it's a type of REM(Rapid eye movement). I get it sometimes when I'm drunk and try to focus on something.I'm not suggesting that you where drunk, but you probably had problem focusing the eyes due to the moving clouds.There is a name for it but I can't find it atm.

Edit: Found it. It's called microsaccade (http://en.wikipedia.org/wiki/Microsaccade)

astromark
2009-Apr-12, 07:40 AM
Well... confusion Raine's supream... but yes its called microsaccade. A look into 'wiki' will help you. Thanks 'Chilinuttz'
In short its an involuntary movement of your eye., and the moment it takes for your brain to catch up with what it did just not see...or did. Its you, not the moon or the clouds. Its not a medical condition you need worry about. Get tired and stare into a mirror., well it worked for me...

JohnD
2009-Apr-12, 11:47 AM
Saccade is a real phenomenon, but I'm sceptical that it is ever perceivable in health.

In the UK, road works are often marked at night by cones with yellow lights on them. The lights are LEDs, that are made to flash to conserve battery power, but at a rate that causes 'flicker fusion' and they appear to shine continuously. If I make my gaze pass rapidly across them, by glancing left to right or vice versa, the flashing becomes easily perceivable. THis is NOT saccading, just deconstructing the flicker fusion at a retinal level.
But as astro says, it's you, not the Moon!
John

TampaDude
2009-Apr-12, 11:35 PM
Thanks, guys...that's probably it...I figured it had to do with sudden eye movements. Anyway, it was an interesting phenomenon.

I know my eyes are okay, though...I just had an eye exam two months ago...no worries.

rommel543
2009-Apr-14, 02:00 PM
I've gotten the same thing when looking at a patterned carpet. The design was that of stacked squares (imagine a grid, with each grid square having 12 squares stacked inside). Because the squares were alternating dark and light colours, and REM, when I stared at the carpet it caused the illusion that the squares were razing out of the carpet, then dropping back in. Kind of a cool effect.

bleuprint
2009-Apr-16, 07:52 PM
it caused the illusion that the squares were razing out of the carpet, then dropping back

When the repetition distance of the squares is less than about 6-4 cm (the distance between your eyes) it could be the same illusion as with "Random Dot Stereograms" (Google it). It happens when your two eyes point (converge) to something behind or before the pattern :shifty:.

Bleuprint

TomBurgessinspace,09
2009-Jun-02, 01:25 PM
lolololo

TomBurgessinspace,09
2009-Jun-02, 01:29 PM
lolololo

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plphy
2009-Jun-02, 06:58 PM
Last night, I was looking at the moon with my naked eyes, with a broken layer of clouds drifting by from right to left at a fairly good clip, when I experienced something strange, [...] The whole layer of clouds would frequently appear to "jump" or "jerk" up and down and sometimes backwards as I watched them. [...] Has anyone else here experienced the same thing as I described it?

I notice this almost every time I see the moon behind thin clouds. I think the microsaccades that have already been mentioned are only one half of the story.

The other ingredient is the Pulfrich effect (http://en.wikipedia.org/wiki/Pulfrich_effect). The eye processes brighter images quicker than dimmer images so that the brain perceives brighter parts of an image slightly earlier than dimmer parts. Due to the eye's saccades the image of the sky is moving slightly around on the retina (while you think you keep looking straight at the moon), and your brain combines a newer image of the bright moon with a slightly delayed image of the dimmer clouds. The movements of the moon and the clouds are thus not precisely synchronised and they appear to move with respect to each other.

This effect is also noticeable when the image movement is not due to saccades but a shaky telescope (http://the-moon.wikispaces.com/page/view/Earthshine/75947709): stars with different brightnesses will appear to shift their relative positions, and the earthshine-lit portion of the young moon will appear to shift with respect to the sunlit part.

You can also see it with non-astronomical objects: watch a distant house projected against the dusky sky with binoculars: due to the slight shaking of your hands, any brightly lit windows will appear to dance within the dimmer outline of the house.

And a bright star close to the horizon during dusk or dawn may often appear to swing back and forth, often quite furiously. A sight that has confounded many an unsuspecting observer (http://articles.adsabs.harvard.edu/full/1889AN....120..109S).

Bye,
Thomas