Mauro, When I was younger I saw the Full moonlit sky as a shade of blue. With age, brunification has reduced my blue sensitivity (increasing my daytime acuity, interestingly), so I see a gray color to the sky with perhaps an imagined bluish tint to the gray (It is a different gray than the gray of my jacket).
I have, however, been at a site dark enough to see the Zodiacal light as yellow (that it was not a contrast effect with the dark blue sky was proved by the close proximity of the Milky Way, which was silver-gray). I also always see the Milky Way in Sagittarius as slightly yellower than the Milky Way in Cygnus. This has been noted by other observers.
As for visual sensitivity and limiting magnitude identification, this is very hard to accurately assess. Visual acuity (a new pair of glasses gave me an extra 1/2 magnitude, for example) and experience have a LOT to do with the visual limit determined with the naked eye. The telescopic limiting magnitude is a little closer in variation, possibly because visual acuity can be dialed in with focusing. But even there, Schaefer's work and my experience seems to suggest a several magnitude range in detection. But that is with a point object (stars), not extended objects like nebulae or galaxies.
A test of several observers at a star party in observation of HII regions in the arms of M33, as well as seeing the extent of the galaxy, varied hugely. In a 12.5" scope (31.8cm), the number of HII regions detected, even among experienced observers, varied from 1 to over 10, and the size of the galaxy from 10' to over 45' (the size of the field of the eyepiece). Everyone knew how to use averted vision. In this case, perception was related, perhaps, to a combination of real genetic differences and experience at looking at objects "at the limit". Many observers do not spend time seeking and looking at objects at the limit, so some of the variation was due, no doubt, to experiential factors.
So, I've found, is the case with faint colors seen through the eyepiece. There is a huge variation in what is seen. However, without suggesting any colors to the observers, several observers saw the same exact colors in the fainter areas of the Orion Nebula on a recent night at a high altitude site--a faint dusty rose in one section and a faint peach color in the other. Here's a picture from Bob Gendler: http://us.st11.yimg.com/us.st.yimg.com/I/spaceimages_1976_8434409 which shows the rosy hue below and to the right of the trapezium area (Huygenian region), and, less obviously, the peach-colored section above the Trapezium region. This picture accents blue, but still shows the subtle colors of which I speak. This picture is alittle better: http://home.earthlink.net/~fct150b/m42.htm and shows the rosy area below the Trapezium region and the peach-tinted area above it. Are the colors real? Well, I can't say the tints perceived are EXACTLY what shows, but close enough to say that Occam's razor would say that the assumption that real colors are seen is a simpler explanation than false colors. Why? Because the tints are too similar to photographic evidence to be dismissed out of hand.
There is a way to test this, though. If the coloration disappears when an O-III filter is added, and reappears when the filter is removed, then real color perception is likely. If, on the other hand, the coloration is still seen with the O-III filter in place, then the colors are false and perception is guided by factors other than perception of real colors.
I intend to perform this test on the next dark of the Moon, with and without the filter in place, and when the nebula is near the meridian to eliminate atmospheric reddening.
And I will report back.
-------------------- Don Pensack
12.5" Truss Dob, 5" Maksutov
Sustaining Lifetime IDA member, TeleVue junkie
Previous
Index
Next
Flat
Re: Is it possible to see the nebula with colour?
Edit
Reply
Quote
