Best Green Star?
Wayne Watson
P.S. Geeze, I actually got a post into this newsgroup despite an ISP that's been giving me lousy
posts for a bit over a month. How long will it last? Ugh.
--
Wayne T. Watson (121.015 Deg. W, 39.262 Deg. N, 2,701 feet)
"Caution. This e-mail message contains minute electrically charged
particles moving at velocities in excess of five hundred million miles/hour."
Web Page: http://www.sirius.com/~mtn_view
Imaginarium Science Museum:
http://www.sirius.com/~mtn_view/imaginarium.html
John Hagan
to the proximity of a red star.
I don't know of any other stars that really appear green. In fact, one
of the best ways to spot small planetary nebulae is to look for their
unusual greenish-blue tint.
John
On Mon, 19 Mar 2001 20:41:48 -0800, Wayne Watson <mtn_...@sirius.com>
wrote:
Mark Wilden
news:3AB6DF8C...@sirius.com...
> Anyone know of a star that is primarily green to the eye?
According to H.A. Rey, in Libra, "the star lowest to the right has a very
faint greenish hue: the only green naked-eye star."
Wayne Watson
mentions it's green. I was just reading about the colors of stars and the author mentioned green is
a hard one to see unless there is a contrasting star in the field. I'll take a look at Rey too.
I've seen a number of stars listed as variations of green, blue-green, white-green, etc.
Mark Wilden wrote:
--
Rod Mollise
>
Hi:
The best example of a star that _appears_ green is Antares little companion.
Peace,
Rod Mollise
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Chris Marriott
There are no green stars. Very cool stars are red; as they heat up they go
from red to orange to yellow to white to blue. No green.
Regards,
--
Chris
-----------------------------------------------------------------------
Chris Marriott, SkyMap Software, UK (ch...@skymap.com)
Visit our web site at http://www.skymap.com
Astronomy software written by astronomers, for astronomers
Doug S.
It's been said that no star is truly green, but many DO look that way, usually
due to contrast effects with a star of a different (usually reddish orange)
tinge. Antares' companion is a good one, but not easy to split in small scopes.
A better candidate, also better placed for northern observers, is Alpha
Herculis (Rasalgethi). It is a fine double whose appearance changes markedly as
the pulsating red supergiant primary varies in brightness. The companion has
always looked intensely green to me when the primary is near maximum, but a bit
more bluish when the primary is near minimum.
Doug S.
Paul Schlyter
> little companion.
*appears* to have that color. All colors are, literally, in the eyes
of the beholder....
--
----------------------------------------------------------------
Paul Schlyter, Swedish Amateur Astronomer's Society (SAAF)
Grev Turegatan 40, S-114 38 Stockholm, SWEDEN
e-mail: pausch at saaf dot se or paul.schlyter at ausys dot se
WWW: http://hotel04.ausys.se/pausch http://welcome.to/pausch
Paul Schlyter
Chris Marriott <ch...@nospam.chrism.demon.co.uk> wrote:
> Wayne Watson <mtn_...@sirius.com> wrote in message
> news:3AB6DF8C...@sirius.com...
>> Anyone know of a star that is primarily green to the eye?
>
> There are no green stars. Very cool stars are red; as they heat
> up they go from red to orange to yellow to white to blue. No green.
it's a contrast effect, but if it appears green then it also "is
green". Colors are, literally, in the eyes of the beholder -- and
you ought to have plenty of personal experience of that!
Paul Schlyter
is all about appearance -- colors are literally in the eyes of the
beholder.
> but many DO look that way, usually due to contrast effects with a star
> of a different (usually reddish orange) tinge. Antares' companion is a
> good one, but not easy to split in small scopes.
get: if you look at it, it appears green.
Chris Marriott
Paul Schlyter <pau...@saaf.se> wrote in message
news:9984nq$t2t$1...@merope.saaf.se...
>
> THere are green stars -- Antares' companion is a good example. Yes,
> it's a contrast effect, but if it appears green then it also "is
> green". Colors are, literally, in the eyes of the beholder -- and
> you ought to have plenty of personal experience of that!
I disagree. I'd say that "colours are in the spectrum of the spectroscope"
and it will show that these stars which appear green are, in fact, not so
:-).
Rod Mollise
>Of course it *appears* green, just like objects of other colors
>*appears* to have that color. All colors are, literally, in the eyes
>of the beholder....
>
Hi Paul:
Take a look, if possible, at the Astronomy Magazine article on this very
subject (March 2001, I believe). You may find it informative. The point is,
that no lone star that I know of LOOKS green--in the eyes of any beholder. The
green is pretty much a contrast effect with multiple stars.
David W Knisely
> Anyone know of a star that is primarily green to the eye?
>
Well, there really is no such thing as a really "green" star, despite
what some texts and people say. Stars emit light much like a
"black-body" radiator, at wavelengths across much of the visible
spectrum. As such, the wide range of colors they emit tend to all blend
together, making what color that is visible to the eye limited in range
and somewhat pastel in saturation. There are reddish-orange, orange,
yellow, yellowish-white, white, bluish-white, and light blue stars, but
no green ones. Some faint bluish stars may appear to be slightly
greenish when sitting right next to a bright yellow or orange star, such
as in the double stars Alberio or Alpha Herculis (especially in a small
telescope), but it is just an illusion caused by the color contrast.
However, some planetary nebulae do appear somewhat greenish when viewed
in a large enough aperture, as they emit strongly in the greenish Oxygen
III spectral lines, but have little emission at other colors. For
example, the "Saturn" nebula (NGC 7009) appears an almost emerald green
when viewed directly in an 8 inch telescope at between 40x and 70x.
Clear skies to you.
--
David Knisely KA0...@navix.net
Prairie Astronomy Club, Inc. http://www.4w.com/pac
Hyde Memorial Observatory:
http://www.blackstarpress.com/arin/hyde
***********************************************
* Attend the 8th Annual NEBRASKA STAR PARTY *
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***********************************************
John Hopkins
news:985099605.16639.0...@news.demon.co.uk...
>
> Wayne Watson <mtn_...@sirius.com> wrote in message
> news:3AB6DF8C...@sirius.com...
> > Anyone know of a star that is primarily green to the eye?
>
> There are no green stars. Very cool stars are red; as they heat up they go
> from red to orange to yellow to white to blue. No green.
Hey, I saw one the other night!
(Of course, I had the broadband filter in.........)
Yers,
/John
http://www.darkhop.com/
John Gretchen
I have Skymap Pro 5 and I've noticed it has Johnson B-V colour index
listings for stars. Is there a way to translate the index number to a
RGB values in nm?
Chris Marriott wrote:
> There are no green stars. Very cool stars are red; as they heat up they go
> from red to orange to yellow to white to blue. No green.
>
> Regards,
>
> --
> Chris
> -----------------------------------------------------------------------
> Chris Marriott, SkyMap Software, UK (ch...@skymap.com)
> Visit our web site at http://www.skymap.com
> Astronomy software written by astronomers, for astronomers
--
Clear skies,
John N. Gretchen III
Port O'Connor TX
http://www.tisd.net/~jng3/stars/ [updated 03/18/01]
"Why are things as they are and not otherwise?"
Johannes Kepler (1571-1630) German astronomer.
Chris Marriott
John Gretchen <jn...@tisd.net> wrote in message
news:3AB7DC62...@tisd.net...
> Chris,
> I have Skymap Pro 5 and I've noticed it has Johnson B-V colour index
> listings for stars. Is there a way to translate the index number to a
> RGB values in nm?
SkyMap Pro 7 displays star colours using the B-V colour index. I don't know
about wavelengths in nm; what SkyMap does is to assign four colour index
reference values to "pure red", "pure yellow", "pure white", and "pure
blue", and then linearly interpolate the RGB values in the three "line
segments" connecting these four points. The user can adjust the four
reference points to adjust the colours.
I'm sure this method is far from exact, but it works pretty well and gives
at least a good approximation to the "correct" colours of the stars. I
believe that Bill Gray uses a rather similar technique in his "Guide"
program.
You can see how this works for yourself, if you want, by downloading the
free SkyMap demo.
Chris Marriott
David W Knisely <ka0...@navix.net> wrote in message
news:3AB7CF66...@navix.net...
> However, some planetary nebulae do appear somewhat greenish when viewed
> in a large enough aperture, as they emit strongly in the greenish Oxygen
> III spectral lines, but have little emission at other colors. For
> example, the "Saturn" nebula (NGC 7009) appears an almost emerald green
> when viewed directly in an 8 inch telescope at between 40x and 70x.
The classic "green" object for me is the Orion Nebula; this looks "apple
green" to me. My colour vision, however, is defective - do other people see
M42 as green, or is it just me?
Paul Schlyter
Chris Marriott <ch...@nospam.chrism.demon.co.uk> wrote:
> Paul Schlyter <pau...@saaf.se> wrote in message
> news:9984nq$t2t$1...@merope.saaf.se...
>
>> it's a contrast effect, but if it appears green then it also "is
>> green". Colors are, literally, in the eyes of the beholder -- and
>> you ought to have plenty of personal experience of that!
>
> I disagree. I'd say that "colours are in the spectrum of the spectroscope"
> and it will show that these stars which appear green are, in fact, not so
> :-).
most people that colors aren't dependent only on the spectrum of the
received light, but also on the detector (i.e. your eye) of this
light!
Paul Schlyter
Rod Mollise <rmol...@aol.com> wrote:
>> Of course it *appears* green, just like objects of other colors
>> *appears* to have that color. All colors are, literally, in the eyes
>> of the beholder....
>
> Hi Paul:
>
> Take a look, if possible, at the Astronomy Magazine article on this very
> subject (March 2001, I believe). You may find it informative.
I'll have a look at it, but I have already read a quite large number
of articles on huma color perception. Science types of people tend to
favor the view that color is some intrinsic property of the light itself,
while e.g. colorimetrists, artists and eye doctors tend to have the
view that color is created within the eye.
> The point is,
> that no lone star that I know of LOOKS green--in the eyes of any beholder.
Are you really 100% sure about that?
Consider for instance Chris Marriot, who is red-green blind. Thus if
he sees a red star, it ought to appear to him to have the same color as
a green star! Therefore Chris could say e.g. "Betelgeuze is green",
and he would be right, because that's what his eyes would perceive.
> The green is pretty much a contrast effect with multiple stars.
Yep -- they are green "In the eyes of the beholder"....
David W Knisely
> THere are green stars -- Antares' companion is a good example. Yes,
> it's a contrast effect, but if it appears green then it also "is
> green". Colors are, literally, in the eyes of the beholder -- and
> you ought to have plenty of personal experience of that!
Funny, the companion to Antares looks a pale blue to me. Its
declination is -26.43 degrees, so it would definitely *not* be well seen
in Sweden (a paltry 4 degrees above the horizon at best for Stockholm;
at least here in southeast Nebraska, it gets up to 22 degrees above the
south horizon). The companions to Gamma Andromdae and Beta Cygni seem
to me to be a nearly robin's-egg blue, so no green seen there either. I
have never really seen stars look anything but the colors mentioned
earlier, and so have a lot of other people with rigorous observing
skills not prone to "illusion". A 'green' star would have to emit light
mainly in the region of from 4900 to 5400 Angstroms (and little
elsewhere in the spectrum) to look really green. No stars do that.
Planetary nebulae do, but stars don't. A person can argue over
semantics until they are "green" in the face, but the facts are that
there are not really any "green" stars.
Rod Mollise
>Are you really 100% sure about that?
Hi Paul:
Having hit middle age and spent a few years on this wacky old planet, Old Rod
ain't 100% sure of much of anything. But I seem to recall that folks with color
blindness have _trouble_ perceiving green (a former boss of mine who was color
blind was never allowed to drive when my colleagues and I were riding with
him--not after a few times of asking us whether a stoplight was green or not!)?
At any rate, to my knowledge, nobody, color blind or not, has started chirping
about "that apple-green star!" :-)
Kruger Kid
through my C8. When I observe in a darker location it is indeed green.
At a very dark location I can see many shades of green and sometimes a
tinsy tad (technical term) bit of red.
Brian Tung
> A 'green' star would have to emit light
> mainly in the region of from 4900 to 5400 Angstroms (and little
> elsewhere in the spectrum) to look really green. No stars do that.
> Planetary nebulae do, but stars don't. A person can argue over
> semantics until they are "green" in the face, but the facts are that
> there are not really any "green" stars.
I think you are brushing over Paul's argument a little too lightly.
In olden times, people used to think that objects emitted light, and
that's how we were able to see them--that their light was inherent in
the object. (Never mind that they were invisible in pitch darkness.)
How is it different to say that color is inherent in the object? If
you illuminate an object in monochromatic light, how will it appear?
Certainly not full color. Very likely, you will at first see it to
be the color of the illuminated light, and then as your eyes grow
accustomed to that light, it will merely appear greyscale.
Now, stars *do* emit light--that makes them different from most objects
on earth, which only reflect light. And they emit, fairly accurately,
black body radiation--not perfectly, but just about. There must be
some stars whose radiation peaks in the green range, between (as you
say) 490 to 540 nm. Sure enough, there are: the class A stars, roughly,
along with some of the late B stars. But ordinarily, these stars don't
appear green--they appear white.
Why? Well, the usual explanation is that there is so much of the other
frequencies along the visual spectrum being emitted along with the
green band that the combination just looks white. Fair enough. But
it turns out that even class O stars have a fairly flat intensity
curve along the visual spectrum. Because of the shape of the black
body radiation curve, class M stars have a sharper peak (in the red)
than other stars, but even they don't radiate nearly solely at the
peak. There is just about as much yellow in an O star, relatively
speaking, as there is red in an A star.
In part, then, it *must* be a perception issue--stars do peak in the
green, just as other stars peak in blue or red. For whatever reason,
our eyes have evolved not to see them as green. And this doesn't seem
to be a trait associated with red-green blindness; I don't know of
anyone who can reliably see the appropriate spectral class *singleton*
stars as green.
Brian Tung <br...@isi.edu>
Astronomy Corner at http://astro.isi.edu/
C5+ Home Page at http://astro.isi.edu/c5plus/
PalmAtlas Home at http://astro.isi.edu/palmatlas/
Doctor Morpheus
[snip]
> The classic "green" object for me is the Orion Nebula; this looks "apple
> green" to me. My colour vision, however, is defective - do other people see
> M42 as green, or is it just me?
Yes, I do as well. But I am afraid the green "tint" on the Orion nebula
may well be an illusion. The eye is more sensitive to green light, so
when you see using the rods, it will most likely appear green.
Regards,
> Regards,
>
> --
> Chris
> -----------------------------------------------------------------------
> Chris Marriott, SkyMap Software, UK (ch...@skymap.com)
> Visit our web site at http://www.skymap.com
> Astronomy software written by astronomers, for astronomers
--
Ioannis Galidakis
<http://users.forthnet.gr/ath/jgal/>
___________________________________________
"If it's green and it moves, it's biology."
"If it stinks, it's chemistry."
"If it doesn't work, it's physics."
"If it doesn't make sense, it's economics."
"If you don't understand, it's math."
[Addendum to Murphy's Laws #716]
Brian Tung
> Yes, I do as well. But I am afraid the green "tint" on the Orion nebula
> may well be an illusion. The eye is more sensitive to green light, so
> when you see using the rods, it will most likely appear green.
Yes, the eye is most sensitive to green. But does that necessarily mean
that objects that emit equally across the board are likely to appear
green? That certainly doesn't happen with bright objects of that sort--
those appear white. It might simply be that the sensors are more
sensitive to green than to blue or red, so that you're more likely to
see a dim green object than a dim red one. That doesn't mean that
you'll see it as green.
There is a known effect where dim objects appear bluer than they really
are. I don't know if that's related to the eye's sensitivity to green.
David W Knisely
> The classic "green" object for me is the Orion Nebula; this looks "apple
> green to me. My colour vision, however, is defective - do other people see
> M42 as green, or is it just me?
Well, at low power, it looks a light blue with a faint greenish tinge.
At higher powers, I can see some green, but it is more of a blue-green
rather than apple green. With the UHC filter, it is "lime" green! One
problem with the nebular lines is that the OIII lines are close to the
"border" between blue perception and green perception, and the H-beta
line is firmly in the blue, so the green saturation tends to be a little
weak. This is one reason why most of the brighter planetary nebulae
appear more green than galactic nebulae like M42, as the planetaries
don't usually have much H-beta emission in comparison to the strong 5007
Angstrom OIII line. Clear skies to you.
Gary Schoetts
being white, or neutral zero on the B-V color index). In these 7
star coloring options is one for plotting those stars that peak
in the green portion of the spectrum, though our eyes would
probably not be able to discern this in real-life observations.
Since green is the color we are most sensitive to, any object
that puts out that much of it we would see only as white. A good
example would be the mantle from a gas camping lantern. That
light source is _very_ green. But look right at it and all you
see is white (or an odd yellowish-green hue that just seems a bit
different from white). I've been into existing-light photography
for many years, so my eye has learned to pick out slight color
variations in white light. Another light source that is very
green is common fluorescent lamps but hardly anyone notices how
strongly they are tinted green. Everyone just presumes them to be
a white light.
I believe that in the other spectral classes of stars, where we
do perceive colors, is that the star has lost so much from the
opposite end of the spectrum that we are better able to see the
peak color of those stars. Green is nearly smack-dab in the
middle. Every white star we see is more green than the others
where we detect colors. We just don't perceive it that way.
Although color films do not accurately mimic slight spectral
variations, I believe they do a pretty good job. Enough so that
anyone who pointed their camera at Polaris all night and taken
the trails of stars on good slide film will very easily see that
some of those star trails are in fact tinted green. I know
because I was amazed when I did that at an early age. Many subtle
star colors that I never saw with my naked eyes at night. One or
two of those trails were a very definite green.
By using Cartes du Ciel anyone would be able to plot out those
stars that do peak in the green portion of the spectrum by
intensifying the green-star plotting color and muting all others.
Then find out by yourself if you can notice "green stars" with
your own eyesight at night. Chances are they will only look
imperceptibly like the color of light from a gas lantern or
average fluorescent bulb (not the newer full-spectrum
fluorescents) a strange shade of white, if any color is noticed
at all.
A particular favorite thing I like about using Cartes du Ciel's
display is that I can fine tune all the colors to very muted
pastel values. Better emulating a true night-sky view. Beta Cygni
(Alberio) and other beautiful double-star combinations actually
look like the view through the telescope when Cartes' many color
display options are adjusted right. It might be interesting to
also use it to show people who have forms of color blindness what
the real sky or colored double-stars look like by intensifying
the colors enough to detect them. It is an amazing piece of
software that continues to surprise me with all its capabilities.
I found it here: http://www.stargazing.net/astropc/index.html
LABourdillon
camping lantern does have some green, it can hardly be categorized as
_very_ green. I've taken night photos using this type of lantern as a light
source, and the colors are definitely in the pink-orange range. From what
you write, a camping lantern should therefore look green when viewed from a
significant distance - it doesn't, it still appears warm-white.
Second, the spectra charts for commercially available fluorescent lamps are
readily available; warm-white, cool-white, etc. Again, while there's green
in the spectrum, this is hardly the dominant color - more blue to the
violet, perhaps. The use of mercury helps adjust the colors, but this
element has become a environmental no-no.
...larry
Gary Schoetts <spam...@noaddress.com> wrote in message
news:fijibt8an0fei5sa1...@4ax.com...
Doctor Morpheus
>
> Ioannis Galidakis wrote:
> > Yes, I do as well. But I am afraid the green "tint" on the Orion nebula
> > may well be an illusion. The eye is more sensitive to green light, so
> > when you see using the rods, it will most likely appear green.
>
> Yes, the eye is most sensitive to green. But does that necessarily mean
> that objects that emit equally across the board are likely to appear
> green?
Yes, "likely" if the light emitted is very weak and does not activate
the cones.
> That certainly doesn't happen with bright objects of that sort--
> those appear white.
Well, it can get quite complicated. Consider the image of the moon, as
seen by a normal individual, for example: The moon's image "appears" to
be colored, but in reality it's not. If you look at the following NASA
photo from one of the Apollo missions taken when the landing probe was
in orbit:
<http://users.forthnet.gr/ath/jgal/Moon3.JPG>
you can clearly see that the colors that the picture shows do not
correspond at all to what we see as the color of the face of the moon
from here.
My position is that the light that reaches us from the moon is not
enough to produce a color stimulus anyway. If someone arguably disagrees
with this, one only needs point at either color photos like the above,
or even earth-based, long-exposed, color photos of the moon.
>It might simply be that the sensors are more
> sensitive to green than to blue or red, so that you're more likely to
> see a dim green object than a dim red one. That doesn't mean that
> you'll see it as green.
> There is a known effect where dim objects appear bluer than they really
> are. I don't know if that's related to the eye's sensitivity to green.
That appears to be correct, and some proof for it is the moon stimulus.
It's not perceived as color, so it appears blue, but on long exposures
it aquires all sorts of other colors.
It does not appear to be true with stars though. It seems that the
pinpoint sources are enough to generate a cone stimulus, since color is
perceived when viewing individual stars.
In the case of the Orion nebula though, I still maintain it's an
illusion and perhaps excepting cases like nebulas which have strong OIII
emissions, I'd say that the stimulus doesn't correspond to anything
real, green, blue or otherwise.
> Brian Tung <br...@isi.edu>
--
Ioannis Galidakis
<http://users.forthnet.gr/ath/jgal/>
___________________________________________
"If it's green or it moves, it's biology."
David W Knisely
> I think you are brushing over Paul's argument a little too lightly.
> In olden times, people used to think that objects emitted light, and
> that's how we were able to see them--that their light was inherent in
> the object.
> There must be
> some stars whose radiation peaks in the green range, between (as you
> say) 490 to 540 nm. Sure enough, there are: the class A stars, roughly,
> along with some of the late B stars. But ordinarily, these stars don't
> appear green--they appear white.
Stars emit light over a broad range of wavelengths, and not just over a
narrow enough band of wavelengths to be perceived by anyone as having
just one color of the spectrum. Early spectral class G (luminosity
class V) stars have their peak emission (top of their Plank curve) in
the green part of the spectrum, and yet, they do not appear green to the
eye (they are either colorless, or an off white). This is because of
the large amount of emission at other wavelengths mixing in. Paul's
argument is somewhat flawed, as it is based mainly on a contrast
"illusion" which not all people see. No stars *by themselves* are green
(which was the point to be answered by the original poster's question).
Only an object with a narrow band of emission ONLY in the green will
appear green (like a planetary nebula). There is an 'illusion' when a
more yellowish or reddish star sits next to a much fainter bluish star,
but it is an illusion which can easily be dispelled by using enough
power to show the stars properly separated, as well as with enough
aperture to properly activate the cones of the eye and allow good color
saturation. The stars themselves do not appear green. The colors of
the stars are somewhat pastel, but they do follow, at least to some
extent, their black body characterisics. I have recently examined quite
a number of the more prominent doubles in my ten inch Newtonian which
have been said to have high color contrast to make my own listing of
them. In not one single case was the fainter companion clearly of a
green color (lots of pretty blues or blue-whites, or even faint reds,
but no greens). A lot of the old "green" double star cases are based on
much older observations with low powers and smaller apertures (or
poorly-corrected achromats). They tend to be somewhat inaccurate. In
fact, one case of alleged color contrast, Omicron Draconis, was said by
one source (STARLIST 2000) to be made up of an orange and blue pair,
when in fact, the primary was a 5th magnitude yellowish G7 star and
fainter star was actually a faint (8th mag.) reddish star itself! I
still see these kind of second-hand stories even in more recent books,
and they just seemed to get propagated on without any updates. I'm
afraid that the myth of green stars is just an illusion and not really a
fact. Clear skies to you.
Bill Becker
Since most of the books I've read list Beta Librae as the star that's
most likely to.....I suggest we all have a look see this year and post
our impressions. I have to admit though that I've never noticed it to
appear green to me in the past...
Best regards,
Bill
Wayne Watson wrote:
>
> Anyone know of a star that is primarily green to the eye?
>
> P.S. Geeze, I actually got a post into this newsgroup despite an ISP that's been giving me lousy
> posts for a bit over a month. How long will it last? Ugh.
>
> --
> Wayne T. Watson (121.015 Deg. W, 39.262 Deg. N, 2,701 feet)
>
> "Caution. This e-mail message contains minute electrically charged
> particles moving at velocities in excess of five hundred million miles/hour."
>
> Web Page: http://www.sirius.com/~mtn_view
> Imaginarium Science Museum:
> http://www.sirius.com/~mtn_view/imaginarium.html
Paul Schlyter
Rod Mollise <rmol...@aol.com> wrote:
> Having hit middle age and spent a few years on this wacky old planet, Old
> Rod ain't 100% sure of much of anything. But I seem to recall that folks
> with color blindness have _trouble_ perceiving green (a former boss of
> mine who was color blind was never allowed to drive when my colleagues and
> I were riding with him--not after a few times of asking us whether a
> stoplight was green or not!)?
from what we do.
Also, so-called "color-blind" people sometimes perceive color
differences which people with so-called "normal" color vision cannot
see. There are e.g. greens which look identical to people woth
so-called "normal" color vision but which appear as different colors
to some people we call "color-blind" --- i.e. people with so-called
"normal" color vision have some color-blindness too! But we never
think about it, and we don't consider it a handicap, simply because
the majority of the people see colors that way. A red-green-"blind"
friend of mine once expressed this as "the borders between the colors
are different from me than from most people".
Paul Schlyter
David W Knisely <ka0...@navix.net> wrote:
> A picky person posted:
>> THere are green stars -- Antares' companion is a good example. Yes,
>> it's a contrast effect, but if it appears green then it also "is
>> green". Colors are, literally, in the eyes of the beholder -- and
>> you ought to have plenty of personal experience of that!
>
> Funny, the companion to Antares looks a pale blue to me. Its
> declination is -26.43 degrees, so it would definitely *not* be well seen
> in Sweden (a paltry 4 degrees above the horizon at best for Stockholm;
almost never dark either. Nevertheless I've seen Antares many times,
and I've even seen it being occulted by the Moon once, here from
Stockholm. And Antares is much easier to see from here than
Fomalhaut!
> at least here in southeast Nebraska, it gets up to 22 degrees above the
> south horizon). The companions to Gamma Andromdae and Beta Cygni seem
> to me to be a nearly robin's-egg blue, so no green seen there either. I
> have never really seen stars look anything but the colors mentioned
> earlier, and so have a lot of other people with rigorous observing
> skills not prone to "illusion". A 'green' star would have to emit light
> mainly in the region of from 4900 to 5400 Angstroms (and little
> elsewhere in the spectrum) to look really green.
against this. The Orion Nebula is another counterexample - visually
it appears green even though its strongest emission line is in the
deep red...
> No stars do that.
There's more to color than just the emitted spectrum.
> Planetary nebulae do, but stars don't. A person can argue over
> semantics until they are "green" in the face, but the facts are that
> there are not really any "green" stars.
Just like there are no stars "really" of any other color either. To
quote you above: a person can argue over semantics until they are
"green" in the face, but the facts are that there are not really any
beholder -- without any eye to watch these objects, there would be no
colors. Consider for instance the wavelengths band of radio, IR, UV,
X-ray -- what colors do stars or other objects "really" have in these
wavelength bands? None of course -- at least not until there are
eyes which could perceive colors from UV, IR, X-ray, etc radiation.
Paul Schlyter
Chris Marriott <ch...@nospam.chrism.demon.co.uk> wrote:
> David W Knisely <ka0...@navix.net> wrote in message
> news:3AB7CF66...@navix.net...
>> However, some planetary nebulae do appear somewhat greenish when viewed
>> in a large enough aperture, as they emit strongly in the greenish Oxygen
>> III spectral lines, but have little emission at other colors. For
>> example, the "Saturn" nebula (NGC 7009) appears an almost emerald green
>> when viewed directly in an 8 inch telescope at between 40x and 70x.
>
> The classic "green" object for me is the Orion Nebula; this looks "apple
> green" to me. My colour vision, however, is defective - do other people see
> M42 as green, or is it just me?
visually through a large enough telescope. But perhaps you perceive
it as greener than most others? The Orion nebula also has a strong
emission line in the deep red (that's why it appears red in many
colour photos), and since you're red-green blind, perhaps you
perceive that line too as green?
Paul Schlyter
David W Knisely <ka0...@navix.net> wrote:
> Paul's argument is somewhat flawed, as it is based mainly on a contrast
> "illusion" which not all people see.
eyes actually work. And this implies that a color of an object
cannot be dteremined solely from the sepctrom of the light emitted by,
or reflected from, that object.
> No stars *by themselves* are green (which was the point to be answered
> by the original poster's question).
of any other color either -- the color is produced by our eyes as a
response to the radiation falling upon it.
> Only an object with a narrow band of emission ONLY in the green will
> appear green (like a planetary nebula).
1. The companion of a reddish star often appears green. Yes, this is
a contrast effect, but nevertheless shows how green can be perceived
by some other mechanism than the one you proposed here as the one and
only possible mechanism for producing a perception of green.
2. The Orion Nebula appears greenish in a lerge enough telescope,
despite that it also has strong emission lines in the blue and the
red.
> There is an 'illusion' when a more yellowish or reddish star sits
> next to a much fainter bluish star,
terminology ALL colors are "illusions". Why not settle for the
more neutral word "perception" instead?
Paul Schlyter
Doctor Morpheus <morp...@hades.org> wrote:
> Chris Marriott wrote:
> [snip]
>
>> The classic "green" object for me is the Orion Nebula; this looks "apple
>> green" to me. My colour vision, however, is defective - do other people see
>> M42 as green, or is it just me?
>
> Yes, I do as well. But I am afraid the green "tint" on the Orion nebula
> may well be an illusion. The eye is more sensitive to green light, so
> when you see using the rods, it will most likely appear green.
the rods don't produce any color preception. Look at any deep-sky
object (except M42 and a few other of the brightest ones), for
instance some galaxies in the Virgo cluster. Do you see them as
green?
Doctor Morpheus
[snip]
> When you see using the rods, you won't see any color at all, since
> the rods don't produce any color preception. Look at any deep-sky
> object (except M42 and a few other of the brightest ones), for
> instance some galaxies in the Virgo cluster. Do you see them as
> green?
Yes. Most of the big M objects that are bright enough for me to see
through my 11x80 have a strange "green" tint. Including andromeda,
lagoon, M13 etc.
The 11x80 are not powerfull enough to see many externals, but in most
cases that I remember, I can detect some sort of strange green tint.
> --
> ----------------------------------------------------------------
> Paul Schlyter, Swedish Amateur Astronomer's Society (SAAF)
--
Ioannis Galidakis
<http://users.forthnet.gr/ath/jgal/>
___________________________________________
"If it's green or it moves, it's biology."
Steve Preskitt
>1. The companion of a reddish star often appears green. Yes, this is
>a contrast effect, but nevertheless shows how green can be perceived
>by some other mechanism than the one you proposed here as the one and
>only possible mechanism for producing a perception of green.
True, but the same effect can be seen with afterimages (which may be
playing a part in the case of "green doubles") - look at a red circle
for a minute or so, then look at a white wall, and you'll see a green
afterimage, but that doesn't mean that wall actually has a green
circle on it. Your point is well taken that perception plays a large
role in what we see, but you can't pin everything to that, otherwise
you'd have to say that trees *don't* make a sound when they fall in
the woods, simply because there is no one to perceive the atmospheric
disturbance it creates. As with many things, there's a middle ground
here - a light source *can* be broken down into a quantifiable
spectrum, but because no two pairs of eyes are the same, no two people
will see it exactly the same way.
Steve
David W Knisely
> Nope! The companion to Antares, which looks green, is one example
> against this. The Orion Nebula is another counterexample - visually
> it appears green even though its strongest emission line is in the
> deep red...
PAUL, THE ORION NEBULA IS NOT A STAR!!!! I doubt you have ever seen the
companion to Antares, and besides, that star does not look green to a
lot of people. The effect is a contrast one. If the companion were
observed at high enough power and with enough aperture, it would appear
the pale blud that most main sequence B stars show. There are N0 green
stars!
jerry warner
every time this subject comes up the same things get saide. One has posted
saying 'old
archives classified and saw green where there was none' under the metaphor 'cave
paintings
aren't Picasso and stone tools arent lasers' - so what! It "proves" nothing. The
fact is I have
seen stars (admittedly few and thats half the fun of searching for them!) which
appeared
"green". Both isolated cases and in multiples. As a rule these were very tiny
specimens and
when powered up faded into soem grayed-green form ........ if not (here's the
key!) dull
red. Viola! I thought about issues of "contrast" and "spectral type" of course -
who worth
salt would not. But then some inner demon grinned and I usually went back to the
view ...
leaving technical matters to the "experts" and the "cultists". (hee hee) The
ancients in their
blindness did list a few "greens" to prove their backwardness and imbecility,
towit:
NORTON'S STAR ATLAS FOR NEANDERTHALS: edition 1910 Im looking at -
OSig67 Camelop. .......... Renmarks: gold and green
32 Eridani ..................... : Topaz and Green. Fine
contrast.
(TOPAZ! HURRAY!!!)
88 Leonis : Yellow and LILAC!
aScorpii (Antares) : red and green (of course!)
As late as 1966 Sky & Telescope was still disseminating the same propoganda with
the
self-same Norton's for sale, undiminished and unbridled .... but that's allowed
from S&T
as prehistory. When debates over contrast and spectral type and who sees what
etcetera
begin in the name of "correctness" , I sometimes wonder if the children will be
saved and
if in the name of survival they will settle this issue once and for all, with
sodium lights!
Frankly, Im now sure who has proven what. I do notice nobody has brought in
atomic physics and stellar evolution. I will wander out into the midst silently
now ... wondering
if a star could be "green" for even an instant. I should not have saide that!
jerry warner
Rod Mollise wrote:
> >Anyone know of a star that is primarily green to the eye?
> >
>
> Hi:
>
> The best example of a star that _appears_ green is Antares little companion.
David W Knisely
posted:
> One has posted saying 'old archives classified and saw green where there was none' under the
> metaphor 'cave paintings aren't Picasso and stone tools arent lasers' - so what! It "proves"
> nothing. The fact is I have seen stars (admittedly few and thats half the fun of searching for
> them!) which appeared "green".
Well, I have never really seen any single stars (high above the horizon)
which appear pure green, although close doubles where one star is yellow
or orangish and the other is deep blue sometimes causes the blue one to
appear to have a slightly greenish tint (like Alberio-B when seen in a
60mm refractor). A faint bluish companion can also seem somewhat
greenish, especially if the observer has previously heard that the star
appears to be green from some text source. At low light levels, color
vision and judgement becomes somewhat inaccurate, so that also figures
into the wide variety of wierd colors reported by the observers of the
late 19th and early 20th century who were using relatively small
apertures for their observations. If you want to know a little more
about the topic of visual star colors in the past, I would suggest
reading COLOURS OF THE STARS by David Malin and Paul Murdin, pages 5-25.