Starman1
Vendor - Scope City
Reged: 06/24/03
Posts: 12230
Loc: Los Angeles
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The yellowing of the lens in the eye, called brunification, slowly filters out the bluer end of the spectrum as we age.
What is blue when we are young appears green as we age.
If the lens starts down the road to opacity (cataracts), not only does the color shift occur, but the brightness diminishes.
When Walter Scott Houston, the veteran writer of Sky & Telescope's Deep Sky Wonders for nearly 50 years, had cataract lens-replacement surgery, his response was that "the world had turned blue". He could now see bluish-white stars and blue-greens where formerly he had seen white or simply greens.
It's a change that comes to us all if we live long enough.
Want to prevent the aging of the lenses in the eye? From childhood, wear dark glasses every minute you are outside when the sun is above the horizon. It appears to be exposure to UV light that causes the changes in the lenses of the eye. At high altitude, try those chrome-plated Highway Patrol sunglasses to reduce the brightness, too.
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Don Pensack
12.5" Truss Dob, 5" Maksutov, Fujinon Binos
Sustaining Lifetime IDA member
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MikeRatcliff
Pooh-Bah
Reged: 06/12/04
Posts: 1329
Loc: Redlands, CA
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That's happening to me. I was looking at some old notes and the Saturn nebula was blue to me 12 years ago (43 yrs old) and now it's definitely green.
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16" f/4.9 dob, 1.25" Paracorr, 24 TV Widefield, 18 Circle T ortho, 13 Nagler T6, 12.5 UO ortho,
9 Circle T ortho, 2x TV Barlow 1.25"
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Luis.E
sage
Reged: 01/30/04
Posts: 280
Loc: Portugal
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In my 10 inch reflector M42 is pale light blue(some nights), and in a area with average light polution.
The Saturn nebula is more blue/grey, but very easy to detect some color.
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" we're just a chemical scum " Stephen Hawking.
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nobody special
sage
Reged: 12/30/08
Posts: 405
Loc: Connecticut
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Don.
I've really enjoyed reading your posts on this subject, thank you.
I'm going to try a little experiment this weekend, weather permitting. I'm going to try to use my digital camera through the eyepiece on Orion, I'm curious if the green I always see will be absent from the picture.
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Tom
Orion XT8 Classic
Hyperion 13mm (With 28mm Tuning Ring)
Orion Sirius 25mm
Meade Series 4000 Plossls 32mm 6.4mm
Orion Shorty Plus 2x Barlow
Telrad
OPT OIII Filter
ND Moon Filter
80a Blue Filter
Smart Seat III
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Starman1
Vendor - Scope City
Reged: 06/24/03
Posts: 12230
Loc: Los Angeles
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Tom,
Be aware that:
--the strongest emission from the nebula is H-alpha, which is red. Our eye is insensitive to this color, but your camera is not.
--we see green because there is also emission at O-III and H-beta, which our eyes see a lot better than H-alpha. It's what is left when the red if filtered out (by our vision).
--so expect to see more reds than greens in the nebula in the photo.
But, blue and green are higher-energy photons (shorter wavelengths), so a short exposure might capture an image closer to what your eye sees than a longer exposure would.
So try a series of exposures of different lengths to see.
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Don Pensack
12.5" Truss Dob, 5" Maksutov, Fujinon Binos
Sustaining Lifetime IDA member
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Javier
sage
Reged: 05/03/09
Posts: 434
Loc: New Jersey
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For me it's a green color with a hint of blue, especially since it's cooling off where I live. Now that the humidity is gone and the air is crisp the Trapezium looked super sharp and I was able to resolve the binary systems within the Trapezium. I'm going to go for it again tonight. I was going to go for the Witch Head Nebula but there was no way to see it with the moon shining. This morning was one of those perfect nights, if I get two in a row I'm a super lucky guy.
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Dave Mitsky
Postmaster
Reged: 04/08/02
Posts: 10519
Loc: PA, USA, Planet Earth
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IC 2118 (the Witch Head Nebula) is a rather difficult visual target. A rich-field telescope (or giant binoculars) probably offers the best chance of seeing it. How dark is your observing site?
http://www.daviddarling.info/encyclopedia/W/Witch_Head_Nebula.html
Dave Mitsky
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Chance favors the prepared mind.
De gustibus non est disputandum.
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Javier
sage
Reged: 05/03/09
Posts: 434
Loc: New Jersey
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Not that dark at all, I just couldn't resist giving it a try.
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scoping
super member
Reged: 01/05/09
Posts: 156
Loc: Jacksonville,Fl
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Quote:
Quote:
If you really let your eyes dark adapt completely, the light of the sky is sufficient to read headlines in a newspaper (and pages in a star atlas). It isn't a matter of making all the lights around you red, it's a matter of making the red lights DIM.
Words of wisdom. The eye has a wonderful power to adapt, if you let it.
One more piece of advice: don't get old. Twenty-five years ago my 10" showed M42 as vivid green. Now it's blue-grey.
Sounds like new mirror coatings are needed.
Mark Kaupas
20"F5
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TenthEnemy
sage
Reged: 01/21/08
Posts: 428
Loc: Maryland
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I just made a quick sketch to show how M42 always looks like to me, very green with some red on the fringe of the brightest area.
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Orion XT10
70mm refractor
12x50 binoculars
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David Knisely
Postmaster
Reged: 04/19/04
Posts: 8290
Loc: Beatrice, Nebraska
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I only see much green in the very brightest central "Huygenian" region. Much of the rest of the nebula is a pale sky blue to bluish-white unless I am using a filter. With the DGM NPB, the colors seem intensified, as at some powers, I can occasionally see a few faint red hues come out from time to time (as it does in the H-Beta filter which has a huge red "leak"). Clear skies to you.
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David W. Knisely
Hyde Memorial Observatory
http://www.hydeobservatory.info
Prairie Astronomy Club
http://www.prairieastronomyclub.org
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Hrundi
Pooh-Bah
Reged: 02/06/08
Posts: 1249
Loc: Estonia
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I wonder if color can be somehow induced by an effect similar to this: http://en.wikipedia.org/wiki/McCollough_effec
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Starman1
Vendor - Scope City
Reged: 06/24/03
Posts: 12230
Loc: Los Angeles
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Quote:
I wonder if color can be somehow induced by an effect similar to this: http://en.wikipedia.org/wiki/McCollough_effect
Well, undoubtedly. This goes a long way to explain why the brain can reverse colors or induce its own where there are none.
And this "false vision" can occur in surfaces too faint to initiate a cone response.
If you see color in any surface that is so faint it is at the limit of your vision, it is induced by that characteristic of our vision that fills in faint colors at the limit.
That image is often cited to be the reason why people often see the colors in M27 reversed (seeing green where, in images, the nebula glows red, and vice versa).
Perhaps that explains the why of faint reds in some faint nebula.
Or, perhaps there is a varying sensitivity to light among individuals. Studies show there can be 10:1 differences in sensitivity to light at the limit(or more), so there is no reason to believe the same doesn't apply to chromatic vision.
Some barriers to believing in faint color vision:
--our vision shifts to the blue during dark adaptation, making reds even more unlikely to see
--the brightness per unit area of some of these nebulae should be below the threshold of human color vision
--the well-researched tendency for the brain to fill in colors where there are none.
Some positives to believing there is faint color vision:
--the colors correspond to photographic evidence
--the colors seen seem to match the wavelength sensitivity of the eye at night(i.e.we see green where the nebula emits both H-a and O-III wavelengths).
--nearly all observers who CAN see the colors see the same colors in the same places.
--the colors are usually seen in the brightest parts, not the fainter parts.
--observers with the most experience tend to see the most evidence of color.
--colors are only seen on the brightest objects, not the fainter ones.
--not all observers see the faint color tints at the same time in the same scope.
--the colors appear stronger and brighter in larger scopes.
So, where M42 is concerned, that many individuals see subtle tints is not too surprising. It is a HIGH surface brightness object.
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Don Pensack
12.5" Truss Dob, 5" Maksutov, Fujinon Binos
Sustaining Lifetime IDA member
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matthew2000tx
sage
Reged: 12/14/06
Posts: 329
Loc: San Antonio, TX
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My wife insists she sees blue and pink. I see a slight blue tint. But no pink.
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<>< Matthew R.
My Astronomy Blog
*16" Meade Lightbridge
*10.1" f/4.5 Coulter Odyessy Dobsonian
*4.5" F/8 Dob. Built by Yours Truly
*3" Celestron First Scope Dob. IYA2009 edition.
*90mm Meade DSX Mak-Cass Go-To
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Lane
Carpal Tunnel
Reged: 11/19/07
Posts: 1515
Loc: Frisco, Texas
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Red and Green cones in the eye need a lot of light to activate them, but the orion nebula is pretty bright in some spots so I can believe reports of some people seeing a hint of these colors. But the blue cones in our eyes are much more sensitive than the reds and greens and can activate in much dimmer light. When I seen the orion nebula in the C11 it is very blue. If you are using an eyepiece with a yellowish tint like the naglers and pentax xw's then that could change the blue color to look more greenish. It could also be a result of the natural yellowing of the cornea in people that choose not to protect their eyes from sun damage with sunglasses as Don already mentioned.
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Mounts: CGEM, ORION SIRIUS, AT Voyager/motorized
SCTs: C6, C8, C9.25, C11,
Refractors: TV Pronto, Orion ED80
Edited by Lane (11/13/09 08:05 PM)
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TenthEnemy
sage
Reged: 01/21/08
Posts: 428
Loc: Maryland
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Quote:
But the blue cones in our eyes are much more sensitive than the ... greens and can activate in much dimmer light.
I thought our sensitivity peaks above 500nm, which is more green than it is blue. Regardless of whether someone sees green or blue in M42, they are seeing O III, which is blue-green.
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Orion XT10
70mm refractor
12x50 binoculars
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Lane
Carpal Tunnel
Reged: 11/19/07
Posts: 1515
Loc: Frisco, Texas
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Here is some good info on rods and cones in the eye.
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Mounts: CGEM, ORION SIRIUS, AT Voyager/motorized
SCTs: C6, C8, C9.25, C11,
Refractors: TV Pronto, Orion ED80
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TenthEnemy
sage
Reged: 01/21/08
Posts: 428
Loc: Maryland
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I don't see anything there that suggests I should be seeing blue in M42. It just seems to say that our blue sensitivity is "comparable" to our green and red despite such a low number of blue cones.
With how green M42 looks to me it's difficult for me to grasp how people see it as blue. I notice very little change in the hue when I use a UHC, it just turns to a richer looking green. When I tilt the filter the nebula becomes red, so it is even bright enough to active the red cones.
Perhaps it's my young eyes, I've had people say it is blue or colorless through my telescope while I was seeing a vivid green.
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Orion XT10
70mm refractor
12x50 binoculars
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David Knisely
Postmaster
Reged: 04/19/04
Posts: 8290
Loc: Beatrice, Nebraska
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Quote:
Quote:
But the blue cones in our eyes are much more sensitive than the ... greens and can activate in much dimmer light.
I thought our sensitivity peaks above 500nm, which is more green than it is blue. Regardless of whether someone sees green or blue in M42, they are seeing O III, which is blue-green.
Well, actually you are seeing several species with M42. The 5007 and 4959 angstrom (bluish-green) OIII lines are pretty strong, but so is H-Beta at 4861 angstroms. In addition, there is some reflection nebulosity from light scattered off of gas and dust originating in the brighter stars in the nebula, so some of the pale bluish coloration often reported visually can come from that as well. I can see that difference when I use a narrowband filter that only transmits the OIII and H-Beta emission lines, as then, most of the nebulosity tends to be a bluish-green color rather than the more pale bluish or bluish-white color I sometimes see without a filter. Everyone sees pretty much what they see with color in M42, and with the variation in color sensitivity between individuals, it is no wonder there sometimes isn't a lot of agreement in what is being seen. Clear skies to you.
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David W. Knisely
Hyde Memorial Observatory
http://www.hydeobservatory.info
Prairie Astronomy Club
http://www.prairieastronomyclub.org
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Hrundi
Pooh-Bah
Reged: 02/06/08
Posts: 1249
Loc: Estonia
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The sensitivity of color vision peaks at 550nm, not 500.
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