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Invisible wrote:
> Sure, they're quite far away (!!), but they're also rather large (!!!),
> and absurdly bright. ;-)
Yep. It would be interesting to figure out how big vs how far away it would
have to be. I mean, the moon is much smaller, the sun is much larger, but
they both look the same size. Actually, I guess it's linear, so it isn't too
hard to calculate.
By the way, I'm pretty sure stars aren't all that bright. I think it's just
because they're large that they seem bright. I.e., per square inch, I don't
think they're a lot brighter than what you can build on earth easily.
(Brighter than street lights, certainly.)
--
Darren New, San Diego CA, USA (PST)
You know the kamikaze monsters in Serious Sam
with the bombs for hands, that go AAAAAHHHHHHHH!
I want that for a ring tone.
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Darren New <dne### [at] san rrcom> wrote:
> By the way, I'm pretty sure stars aren't all that bright. I think it's just
> because they're large that they seem bright. I.e., per square inch, I don't
> think they're a lot brighter than what you can build on earth easily.
> (Brighter than street lights, certainly.)
I think that getting something to be 6 million times brighter than the
Sun can be pretty hard...
http://en.wikipedia.org/wiki/Cygnus_OB2-12
--
- Warp
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Warp wrote:
> I think that getting something to be 6 million times brighter than the
> Sun can be pretty hard...
Note that I said "per square inch." Sure, if your star is 92x as big as
the Sun, it's going to be very bright in an absolute sense.
100x the heat of the *middle* of the Sun:
http://www.msnbc.msn.com/id/11732814/
Even the middle of lightning gets 2x as hot as the (presumedly, surface of
the) star you referenced.
As I say, it's all about square inches. The *middle* of the sun is
15,000,000K. The surface is 15,000K. Big difference.
Since a star's surface is essentially a black body, it's pretty easy to
calculate the temperature of it, and other black bodies the same color will
be about the same temperature. So the hottest parts of lava are about the
temperature of the sun's surface, and the hottest parts of a propane flame
are about the same temperature as a blue star.
--
Darren New, San Diego CA, USA (PST)
You know the kamikaze monsters in Serious Sam
with the bombs for hands, that go AAAAAHHHHHHHH!
I want that for a ring tone.
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Darren New wrote:
> As I say, it's all about square inches. The *middle* of the sun is
> 15,000,000K. The surface is 15,000K. Big difference.
Sorry. Should have been 5K, not 15,000K. Indeed, ignore that whole sentence.
Anyway, Sun's surface temperature: 9800F.
Industrial tools: 25,000F.
http://www.x20.org/industrial/plaz50.htm
For $1300 you can have something >2x the heat of the sun in your hand.
--
Darren New, San Diego CA, USA (PST)
You know the kamikaze monsters in Serious Sam
with the bombs for hands, that go AAAAAHHHHHHHH!
I want that for a ring tone.
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"Invisible" <voi### [at] devnull> wrote in message
news:4b0c0220$1@news.povray.org...
> I just noticed the other night that as I passed under a sign telling me
> the motorway exit was in 1 mile, I could already see the green traffic
> lights beyond the exit. And those lights can't be much more than 24cm
> across...
Now calculate the angular extent of most distant star you can see with the
naked eye and explain your mistake <g>.
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"somebody" <x### [at] ycom> wrote in message news:4b0c9afb$1@news.povray.org...
> Now calculate the angular extent of most distant star you can see with the
Never mind. I should learn to read the rest of the thread.
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> This is what I'm interested in. Are the lights visible from this distance
> because they glow? Or would any old object be visible from such a
> distance? (Assuming it wasn't the middle of the night, obviously.)
The fact that it is dark helps a lot, obviously your eye is much more
sensitive then.
According to this page:
http://math.ucr.edu/home/baez/physics/Quantum/see_a_photon.html
A rod in your eye must receive about 5-9 photons over 100 ms to tell your
brain that something is there. That is a pretty damn small amount of light.
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scott wrote:
> According to this page:
>
> http://math.ucr.edu/home/baez/physics/Quantum/see_a_photon.html
>
> A rod in your eye must receive about 5-9 photons over 100 ms to tell
> your brain that something is there. That is a pretty damn small amount
> of light.
And THAT is why when it's dark, everything seems "sparkly", I presume.
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On 11/24/2009 11:11 AM, Invisible wrote:
> This is what I'm interested in. Are the lights visible from this
> distance because they glow? Or would any old object be visible from such
> a distance? (Assuming it wasn't the middle of the night, obviously.)
I would guess that stars are significantly distant enough that their
angular diameter is too tiny to be visible without the aid of the light
they give off.
--
Michael Horvath
mik### [at] gmailcom
http://isometricland.com
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OK, so according to the best data I could get my hands on, Alpha Centuri
A is about 430 light years away, and is 1.227 times the radius of our
Sun, so about 853,400 km across. 430 light years is 4.068x10^15 km.
So, if a triangle has sides of 4.068x10^15 km and 853,400 km on either
side of the right angle, what *the hell* is the small angle?!
By the looks of things, dividing these two distances should give me the
tangent of the angle I seek.
853,400 km / 4.068x10^15 km = 2.098x10^-10
arctan 2.098x10^-10 = 1.2020x10^-8 degrees = 4.327x10^-5 arc seconds
This is a *stupidly tiny number*. If you asked POV-Ray to render this,
and you sent out a million, billion, trillion rays, every single damned
one would completely miss such a tiny object. It seems astonishing to me
that such an absurdly minute object is visible at all - but Wikipedia
claims it is...
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