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Mount Wilson Solar Seeing Scale

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Seeing is quite easy to describe. Basically it boils down to how clear and transparent the sky is. Most solar imagers, pro and amateur alike use the Mount Wilson scale to quantify their seeing conditions. The Mount Wilson scale ranges from 1 to 5 with one being the absolute worst conditions, and a five being pristine.

ONE on the Mount Wilson scale signifies very bad seeing, the absolute worst conditions you can imagine, with boiling so rampant it's difficult to see or even focus an image and with the limb resembling the teeth of a circular saw blade. If you have a ONE seeing, don't even go outside. Stay home and do something constructive with your time.

FIVE on the Mount Wilson scale, on the other hand, represents almost perfect conditions. Video captures will look like still images. Focus will be tack sharp and there will be no scintillation whatsoever anywhere throughout the image. And a THREE on the Mount Wilson scale would pretty much signify average seeing conditions. A THREE is what many of us will encounter on a pretty consistent day-to-day basis.

The Mount Wilson scale quantifies seeing by attraching a number to it and relating each point on the scale to Resolution in Arc Seconds.


Mt. Wilson Solar Seeing Scale:


1 = Solar image looks like a "Circular Saw Blade." Completely out of focus. Limb motion and resolution greater than 10 arcsec. Smaller sunspots will not be seen.


2 = Solar image is always fuzzy and out of focus. No sharp periods. Limb motion and resolution in the 5 to 10 arcsec range.


3 = Solar image about half the time sharp and half the time fuzzy. Some short periods where granulation is visible. Limb motion and resolution in the 3 arcsec range.  


4 = Solar image more often sharp than not. Granulation almost always visible. Limb motion and resolution in the 1 to 2 arcsec range.


5 = Solar image looks like an "engraving." Extremely sharp and steady. Limb motion and resolution 1 arcsec or better.


Note: Observers may use fractional values if the image quality falls between any of the above definitions.

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