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Science Forum Index » Astro Forum » Scientist quantifies the darkness of outer space
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| Dr. Doolittle |
 Posted: Wed Feb 07, 2007 9:51 am |
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Quote: From Mathaba News Network:
http://www.mathaba.net/0_index.shtml?x=549756
When Neil Armstrong and the astronauts that followed after him were on
their way to the moon back in the late 1960s and early 1970s, they
were surrounded by a dark void, virtually of infinite size and scale
in all directions. Apart from those rare moments when their gaze
happened to be directed towards the nearby sun, the earth or the moon
in the sky, they will have seen nothing but tiny pinpricks of stars
set against this engulfing blackness of infinity all around. Thinking
on another level, if we were to travel out of our Solar System on an
imaginary voyage toward the nearby stars, all light coming from the
sun would gradually fall out of the equation. But just how bright
would space be when we're sailing between the stars? We know it's
extremely dark out there, but just how dark is very dark?
Now a UK based scientist claims to have found the answer. Abdul Ahad,
a freelance astronomer and sci-fi author has produced an article that
tells us just how much star light the universe is sending our way, if
we exclude all light coming from the nearby sun. According to his
calculations, it comes to roughly 1/300th of a full moon's worth. Some
of his colleagues and fan club have even coined it "Ahad's constant".
Here's how he went about doing the complex mathematical computations.
Astronomers measure the brightnesses of stars across the night sky
using something called the magnitude scale, first introduced by the
Greek astronomer Hipparchus in the second century B.C. The scale in
itself can be somewhat confusing, since a first magnitude star is
actually brighter than a second magnitude star, opposite to what you'd
expect going purely by every day common sense. You can learn more by
searching Google for 'magnitude scale for star brightnesses'.
Suppose we have two stars of magnitudes M1 and M2. Then their
luminosities L1 and L2 are related by the formula:-
L2/L1 = 10^[0.4*(M1-M2)]
The luminosity of the pair of stars is L1 + L2 = L1(1 + L2/L1), and
their combined magnitude is then given by:-
Mc = M1 - 2.5*log10 (1 + L2/L1)
For the general case, where the magnitudes of "n" stars need to be
aggregated, we can generalise this by computing all the ratios:-
Li/L1 = 10^[0.4*(M1-Mi)] for all stars i from 2 through n. The
combined magnitude is then:-
Mc = M1 - 2.5*log10 (1 + L2/L1 + L3/L1 + ... + Ln/L1)
"Ahad's constant" is simply defined to be the sum of all the
individual magnitudes of every single star across the entire night
sky, right down to the faintest star that could ever be seen with the
most powerful telescope ever invented or is likely to be invented in
the future. In other words, the value of "n" in the above formulae
(i.e. the star count) will tend to infinity. Based on Ahad's numerical
integrations, he has found that as n tends to infinity, the variable
Mc in the above equation tends toward a bottom line figure of some
-6.5 magnitudes (1/300th of a full moon equivalent worth of light -
the so-called "Ahad's constant").
Abdul Ahad commented: "It can be appreciated by someone sailing more
than a couple of light years beyond the neighbourhood of the Sun in
any direction. When you're that far out, you'd want certain physical
barometers to pinpoint your overall 'existence'" he went on, "One of
them might be knowing whether the environment your ship is sailing
through is a complete vacuum. Another might be knowing your distance
from the next nearest planet or star. Yet another might be to know how
much net starlight the sky is providing. It will remain an invariant
celestial constant to a traveller located in deep interstellar space
within several hundreds - if not thousands - of light years from here.
All that humanity can ever hope to physically experience or
meaningfully contemplate over within the foreseeable future of our
species..."
Stars in the neighborhood of the sun are extremely feeble in their
intrinsic brilliance - most of them being tiny red dwarves of < 0.1 x
sun power - and the average spacing between them is approximately 5
light years. Hence, 99.9% of the time during an interstellar voyage
between any two stars in this part of the galaxy, you will be
travelling under the feeble illumination quantified by "Ahad's
constant":
As we venture outward from our Solar System, the sun would diminish in
its apparent brightness, much like how the green light from a traffic
signal gradually fades to a star-like point in the rear view mirror
inside a car, as it pulls away.
By working out a point in space where the sun's light intensity
becomes exactly equal to that of the surrounding cosmic illumination
of -6.5 magnitudes, Abdul Ahad has defined an imaginary sphere. That
has now become generally known in Physics and Astronomy circles as the
"Ahad Sphere of Solar Illuminance", and its radius extends
approximately one trillion miles or about eleven thousand five hundred
astronomical units outward from the sun.
-Abdul Ahad is a member of the British Astronomical Association in the
UK and the Planetary Society in America. He is also the author of a
popular new sci-fi series called "First Ark to Alpha Centauri", where
he makes references to his above astronomical findings in a science
fiction context. |
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| Greg Neill |
| Posted: Wed Feb 07, 2007 10:06 am |
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"Dr. Doolittle" <doolittle@rock.com> wrote in message
news:1170856261.293303.53200@a75g2000cwd.googlegroups.com...
[snip]
Back for another round of sock puppetry are you Abdul?
You posted exactly the same thing under a different sock
puppet last year. |
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| Guest |
| Posted: Wed Feb 07, 2007 11:09 am |
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On Feb 7, 2:06 pm, "Greg Neill" <gneill...@VEsympatico.ca> wrote:
Quote: "Dr. Doolittle" <doolit...@rock.com> wrote in message
news:1170856261.293303.53200@a75g2000cwd.googlegroups.com...
[snip]
Back for another round of sock puppetry are you Abdul?
You posted exactly the same thing under a different sock
puppet last year.
You can leave your comment on my blog:
http://www.openmindsblogspot.com/HOME/tabid/36/EntryID/24/Default.aspx#Comments
Emdad |
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