On Wednesday 21 December 2005 15:42, Pat Naughtin wrote:
> Dear All,
....
> >From what distance can lightning be seen?
A rough rule of thumb for estimating distance to the horizon for
visible
light is based on the height of the source. If that is given in meters as h,
then the distance d is given in kilometers by d=3.84sqrt(h). For "close
enough" call it 4sqrt(h). Of course, the brightness of the lightning bolt and
the brightness of ambient light will be factors as well. It is reasonable to
believe that lightning can be seen farther away at night than at daytime.
Sprites, which are upward traveling lightning "bolts" can be seen above
thunderstorm cells from mountain tops long distances across adjoining plains
and even from the Space Shuttle Orbiter while in orbit! The sprites are
probably not as bright as the main bolts thought to be associated with them.
> >From what distance can thunder be heard?
Googling this question brought up a page that claims the typical limit
for
the thunder to travel and still be heard is 10 miles. I suspect that's in the
ball park of 15 km, or so. The page I found was
http://starryskies.com/articles/dln/5-00/lightening.html
While I'm on this topic, the latest thinking is that most lightning is
caused
by cosmic ray particles which cause an avalanche of electrons traveling at
relativistic velocities. Otherwise, calculations suggest, the "spark" would
be quenched by atmospheric gases before reaching ground or distant clouds.
Recent articles on this have appeared in Physics Today (carried by many
libraries) and in IEEE Spectrum.
Jim
--
James R. Frysinger
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