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> I'm not sure you'd see a point source. You need enough surface that the
> likelihood of multiple photons reaching your eye in a short interval is
> positive.
If the point source was emitting photons at the same rate as a star though,
I don't think you'd be able to tell the difference between the star and such
a point source.
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Invisible wrote:
> I have never, ever, in my entire life, seen anything that remotely
> approximates this, except on TV and in posters.
Like that line in Madagascar, when they're still in the New York Zoo.
"Oh, look, the star is out!"
"Whoops, nope, just a helicopter."
--
Darren New, San Diego CA, USA (PST)
Human nature dictates that toothpaste tubes spend
much longer being almost empty than almost full.
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Invisible wrote:
> I doubt your eyes can see single photons anyway...
Somewhere between 5 and 10 over the course of 100 ms, for humans.
> Well, the books seem to claim that it *is* caused by waves,
Those books are wrong. It's the same *math* as waves, but it isn't waves.
> babble some nonesense about a "quantum superposition of states" to make
> up for the fact that this explanation makes no sense at all.
It's only nonsense if you don't know what it means.
--
Darren New, San Diego CA, USA (PST)
Human nature dictates that toothpaste tubes spend
much longer being almost empty than almost full.
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>> babble some nonesense about a "quantum superposition of states" to
>> make up for the fact that this explanation makes no sense at all.
>
> It's only nonsense if you don't know what it means.
"And the waves interact to generate these interference patterns."
"OK, so why do I still get the exact same patterns if there's only one
photon there?"
"Um... right, OK... that's because there are these extra versions of the
photon, that all exist at the same time. They generate the interference
pattern. Oh, but you can't measure them, see? Because as soon as you
look at them, they stop existing, right?"
"Dude... WTF?"
--
http://blog.orphi.me.uk/
http://www.zazzle.com/MathematicalOrchid*
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Invisible <voi### [at] dev null> wrote:
> > City lights are annoying here, but
> > that picture looks like what I grew up seeing.
>
> I have never, ever, in my entire life, seen anything that remotely
> approximates this, except on TV and in posters. Every time I see
> something like this in films it looks like over the top CG, because real
> skies never, ever look like this.
Skies look like this in most places in the world (clouds and moon permitting, of
course!), considering how relatively sparse human population centres are. Just
think of all that ocean, too!
You can definitely see skies like this in many locations in the UK. You'll see
good skies within 50 miles of MK. But you do need to make the trip!
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Sabrina Kilian <ski### [at] vtedu> wrote:
> Bill Pragnell wrote:
> > Any expert photographers here want to comment?
>
> Servo motors work wonders, when you can gear them correctly.
>
> There are several tripod heads designed to track correctly against the
> spin of the earth, allowing for long exposures. Anything that works for
> for automatic telescopes can do the same work for a camera.
Yah... as Scott said, if it was done with a tracking mount then it must be a
composite, because both sky and ground are in focus.
I must try some sky photography sometime, though. :)
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scott wrote:
>> You can also buy telescope tripods that will use a small motor to turn
>> the telescope in counterpoint so the stars appear stationary. I
>> imagine the same would work for a camera, and then it would be the
>> ground that's blury.
>
> That was my point, I know how to keep the stars sharp or to keep the
> ground sharp, but how to get both in the same photo?
>
>
With a camera, the trees are going to move relatively little if you are
tracking stars relatively high in the sky. And that little bit they move
will be hidden by the stars that take up the field of view where the
tree was before.
Tracking a star at the horizon would be more difficult. I would have to
think of a good trick there that doesn't involve just cropping or
zooming in on only stars.
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Invisible wrote:
> I doubt your eyes can see single photons anyway...
If the photon hits a rod cell in the eye, then yes. Whether the brain
would process this over the photon flux of your surroundings would be up
for question. In total darkness, I think you would see it.
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Sabrina Kilian wrote:
> Invisible wrote:
>> I doubt your eyes can see single photons anyway...
>
> If the photon hits a rod cell in the eye, then yes. Whether the brain
> would process this over the photon flux of your surroundings would be up
> for question. In total darkness, I think you would see it.
It's true that in very low light conditions, vision takes on a
"speckley" character, presumably due to some combination of small
numbers of photons or small numbers of individual nerve impulses
generating a fairly noisey signal. I'm not sure whether one single
photon is enough to generate a nerve action potential though; maybe it
takes 10 or so?
--
http://blog.orphi.me.uk/
http://www.zazzle.com/MathematicalOrchid*
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Orchid XP v8 wrote:
>>> babble some nonesense about a "quantum superposition of states" to
>>> make up for the fact that this explanation makes no sense at all.
>>
>> It's only nonsense if you don't know what it means.
>
> "And the waves interact to generate these interference patterns."
>
> "OK, so why do I still get the exact same patterns if there's only one
> photon there?"
You don't get the interference pattern with only one photon. You get it
if you sum a lot of photons emitted one at a time. A single photon will
still hit only one place*, but that place is more likely to be in one of
the locations that you would expect from a wave.
Many-Worlds Interpretation not withstanding.
> "Um... right, OK... that's because there are these extra versions of the
> photon, that all exist at the same time. They generate the interference
> pattern. Oh, but you can't measure them, see? Because as soon as you
> look at them, they stop existing, right?"
>
> "Dude... WTF?"
>
Not quite the same, but how can a 4D object interact with it self in 3D
space?
Photons are not waves, but their position is governed by a waveform that
represents the probability that the particle will be at any given point.
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