Re: Planet X: MAY Coordinates
Bob May wrote:
>
> You really should learn the proper words to use to describe things. But
> then again, this is all a fraud and you know it. Professional telescopes
> don't have any "zoom" controls on them and can't "set" the magnitude with a
> specific control. Not only that, but you have so little knowledge of
> astrophysics that you don't even know how to specify an object's position.
>
> --
> Bob May
> Remember that computers do exactly what you tell them to do, not what you
> think you told them to do.
This, of course, *deliberately* misses the point. The bottom line is
that you do not wish to deal with Nancy as a credible point of view.
Having made that decision, you can squabble over semantics and the exact
meaning of words and otherwise climb up on a self constructed pedestal.
Her absence of a scientific background and the improper terminologies
allow you argue snobbery and thereby totally miss the point.
I don't have access to Nancy's mind but I can speculate what she means,
and so could you. What the word "zoom" means is not to adjust the "zoom
knob" on your 200" back yard newtonian, but to adjust the image controls
so that your eyes can be an asset and not a liability.
The upper limit on visual acuity in the human being is about 30 seconds
of arc. This is an ideal upper limit and is based on a monochromatic
light (to avoid chromatic aberration) and ideal focus. The average
reality is much worse and if you need glasses there is yet even more
factors to consider. The bottom line is that the eyeball is not a
particularly good astronomical imaging device. There are other issues.
The fovea has an absence of rods, which are the most sensitive to light,
and the most central region of the fovea has a peculiar lack of cones
sensitive to blue. All in all, it makes for a highly uncalibrated
situation. This is why astronomers use telescopes. (Duh.)
Telescopes, like eyes, are limited by *their* optical performance, and
for many of the same reasons. One of the more important measures is the
point spread function which is a two dimensional impulse response. An
impulse is a mathematical abstraction with infinite amplitude, zero
width, and an integral value of 1. There is no such thing as an
impulse, but it allows engineers to do useful calculations (like compute
the point spread function). There is a fundamental limit, the
diffraction limit, that depends on the aperture (or diameter) that
limits the point spread function. We (the collective human we) are
getting very good at making optical components and it is relatively
common for even amateur telescopes to be diffraction limited. The
bottom line is that, regardless of what the limits are caused by, the
point spread function limits what can be resolved in principal.
Modern equipment uses CCD imagers because they offer geometric
precision, a high S/N ratio (particularly when chilled), good quantum
efficiency, and the ability to be individually characterized for
performance (gain and offset errors), even on a pixel basis.
Measurements are repeatable, at least to the limit of the quantum
noise. A pixel in a CCD is a certain size, and one of the clear
parameters of interest is mapping the pixel size to the inherent
resolution of the telescope. Clearly you do not get useful data from
having one giant pixel image the entire sky, nor do you get *meaningful*
data from too many pixels because of the point spread function. If the
point spread function goes over many pixels the resulting picture is no
better, just more spread out. Depending on the magnification (and don't
tell me that telescopes do not have magnification), the pixel size of
the CCD will be "goldilocks" mapped to the point spread function - not
too big, not too small. This magnification means that each pixel of the
CCD subtends some arc in the sky, and I'm willing to bet that that arc
is *much* smaller than 30 arc seconds (the approximate human limit).
Now to be fair, if a pixel were to represent, say, .1 arc second of
resolution in the sky, and your statement about the lack of zoom were
literally true, the picture would have to be presented to an eyeball at
the same .1 arc second. This, of course, would not be particularly
helpful.
The fovea (the center of the visual field where the detail is greatest)
subtends an arc approximately equal to the finger nail of your little
finger when held at arm's length. You gain the most amount of
information about something when it matches the size of the fovea well.
If the image is too big, you can only see it in context with your
peripheral vision and if it is too small, well, it is too small.
Whether or not you are looking through the lens or at a photograph or
other printout, your ability to interpret what you see will depend on
matching the thing of interest to the approximate diameter of your
foveal vision.
So using many fewer words, what Nancy *means* is "adjust the display of
the image to a size that allows your eye/brain combination to work
well". This, of course, assumes that your brain is sufficiently open to
even accept what your eyes tell you, but then again this assumes that
you have even read this far. Probably you saw that this was about Nancy
and just assume I am a troll. So be it.
So: zoom means how it is presented to your eye, not the "zoom" knob.
(But then again, you already know this...)
The second issue has to do with the "magnitude adjustment". Again,
there is some very clear and well understood science here.
A CCD is not a photon measuring device, it is an electron counter. A
photon impinges on the surface and creates a photo-electron, which is
captured in the potential well under the CCD surface. With a
sufficiently bright source or a sufficiently long time a number of
electrons are accumulated in the well and these are read out by the
interface electronics and presented to computers and humans via
displays.
Two things conspire to interfere here. First is thermal noise. There
is a probability function of the absolute temperature which says, in
essence, that there is a random chance one of those electrons will just
appear there seemingly all by itself. This means that a CCD will
accumulate charge even in the total dark. This is called "dark current"
and is annoying. (This is why the CCDs are often super-cooled.) In
addition, the photon capture function is also probabilistic. This means
that there is some chance that any photon will generate no electrons, a
single electron, or two. This is referred to as quantum noise, and
cannot be eliminated in principal. The quantum noise is equal to the
square root of the number of electrons. If there is one electron, the
quantum noise is one and your S/N is 1. (This is bad). If there is 25
electrons, the quantum noise is 5 and your S/N is 5. (Very noisy). If
there is 10,000 electrons, the quantum noise is 100 and your S/N is
100. (Much better).
These effects also occur in your eyeball because the physics is the
same. The reason you do not see it is because your brain is doing you
the courtesy of performing spatio-temporal filtering. In fact, your
vision is not just worse at low light, it also "runs slower". It takes
your brain *longer* to figure out what you are looking at when it gets
few photons, and this effect has been studied and quantified. This
effect was also used to create a novel "3D" image during the Super Bowl
half-time show about 10 years ago. (You had to wear these funky glasses
that had one eye much darker than the other.)
The bottom line is that equipment produces much better images (i.e.
lower noise) when it has a lot of electrons to measure. Having a lot of
electrons means having either a bright source or a long exposure time.
Since the thingy in question is stated as being rather dim, a long
exposure time is most likely to show what, if any, detail there is to be
seen.
Of course, long exposure times and bright sources produce a conflict.
The well in the CCD is only so deep, and once it fills up, it fills up.
This produces a saturation effect. Even worse, if you keep trying to
fill up the well, the electrons can bleed over into adjacent pixels and
corrupt them. This is called blooming. Hopefully, one wants to image
either all bright sources or all dark, not both at the same time. Also
hopefully, a dark region one wants to image is not directly adjacent to
a bright image or the blooming will wash it out. This is the reason why
there have not been any images of planets around other stars, even if
you could *resolve* it you still cannot image it because of the huge
dynamic range.
In addition, beautiful Hubbell pictures to the contrary, this noise
effect also shows up in any kind of display that a human might use to
look at a picture, a monitor, LCD display or even photograph. It is
easier to see subtle variations on a bright background than a dim one,
and the noise is why. Dim backgrounds produce little light and your
brain has to work harder (and slower) to interpret what the image is.
This is why most "hard core" astronomical images are negatives, the
subtle points are bright and really stand out.
Now why would there be confusion as to the apparent magnitude? Well
remember, there are supposed to be critters living on this thingy, and
these critters are somewhat like our critters. This means that the
overall surface temperature cannot be much higher than something around
300K, which is decidedly cold for a black body radiation source. The
black body spectrum is going to be deep in the infrared. Now also it is
stated that this object glows sufficiently that the critters on this
thingy can *see*. This means that there is a light source in the
visible range, but it clearly cannot be black body, it must be some kind
of complex spectrum which is related to the causal mechanism. Since we
are not sure just what causes this thing to glow in the visible light,
we have no information. Either way, if this thing is what she says it
is, it is extremely clear that we are not looking at a "standard" black
body radiator. Normal objects that we see are either decidedly black
body with emission and absorption lines (like the sun) or black body
with a reflected albedo of another black body (like the moon). Since
this thing is far away, the reflected albedo from the sun is likely to
be somewhat low, clearly lower than its natural radiation, which is
obviously a non typical spectrum.
So again, what Nancy *means* by adjust for magnitude 10 is "use an
exposure time commensurate with a magnitude 10 object even though a
strict photometric measurement would probably show a magnitude 2 because
the spectrum is not what you think it is".
And oh, by the way, post the negative, not the positive on
alt.binaries.pictures.astro so it is easier to see subtleties. A
previous poster had a "picture" on a web site which purportedly showed
that there was nothing there. It was a fine graphic, but unfortunately
it was not a picture. A picture would have had noise in it, and a
usable picture would have been a negative, not a positive. It was,
however, a fine graphic of a star chart.
But I'm reasonably sure you have not read this far and even more sure
that you won't actually take the picture and post it. After all, you
just think I am a troll and uneducated in science.
The Small Kahuna <person@company.com>
