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[Phys-L] Re: Light from fireball visible?



Interleaved:

Hugh Haskell wrote:

At 09:43 -0800 2/8/06, Bernard Cleyet wrote:


A friend asks if the Nagasaki was visible, as reported in "The Empire of
the Sun".

I calculated the distance from the top of the fireball to the horizon
(~70 kM) and found it ~ < 1/10 th the distance to Shanghai. (800 Km)
Using the same data at Frenchman Flat, I get Vegas as about twice.
Vegans saw a glow from the tests.

Was the author using lit. license?



I don't know the exact size of the fireball, but the bomb detonated
at about 1900 ft ASL, and didn't touch the ground, so that limits the
fireball height to no more than 4000 ft. ASL.

Glasstone: 1640 ft + Fireball radius 712 ft = 2352 ft

<>The northern half of
Kyushu Island, where Nagasaki lies is quite mountainous, so it is
unlikely that the fireball itself was visible even as far as the
horizon from 4000 ft.

Is on the west coast, middle of the island. In the direction to
Shanghai, the highest part of the mountain ridge (SW of city) is 1500
ft (GOOGLE Earth). This is irrelevant, just being picky.

<>Could the glow be seen from 800 km? I doubt it.
There are no reports of the glow of Trinity being seen from that
distance, and it was about the same yield as Nagasaki, and also
nestled among surrounding mountains.


This was my conclusion, also. Tho the ball had 100 X luminosity of
sun. [Aside: To equal the sun, necessarily viewed from high altitude,
one would need be 10 times distant from the ball when it subtends one
half degree. I obtain ~ 3 k miles.] From Shanghai visibility would
depend on ideal Mie and Rayleigh scattering.

Vegas is only about 150 km from Frenchman's flat, and there are lots
of reports of the atmospheric tests in Nevada being seen from Vegas,
but I don't recall and reports of fireballs being seen from there.


Right, one must drive half way to ground zero, as I wrote.

When they moved the tests underground, however, there were lots of
reports of dishes being rattled by the blasts, and a few of broken
dishes or glass.

It appears that the author was indeed using literary license, or the
protagonist had somehow been transported to the coast of Korea, where
the glow might well have been visible, although I have heard of no
such reports (but I also don't know if anyone has ever asked that
question).

Another aspect that would prevent the glow from being seen from
Nagasaki, was the time of day. IIRC, the Nagasaki bomb detonated
around 11 AM, which would have made the glow quite muted on top of
the normal daylight. If conditions were just right, a pre-dawn
detonation might have been seen at that distance, but I still doubt
it. Reports of people seeing the glow from Trinity from over 100
miles away are common, but that happened just before dawn (5:30 AM),
so there was little background light to drown it out. In fact, most
of our tests (but not all) were done at night or in the pre-dawn
twilight, probably to enable more definitive pictures to be obtained.

Hugh


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Hugh Haskell
<mailto:haskell@ncssm.edu>
<mailto:hhaskell@mindspring.com>

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