Re: [magnitude6] for your amusement (fwd)

[Jan Hollan <jhollan@amper....muni.cz>]

> Russian astronauts on the international space station claim they are being
> dazzled by lights from Britain's tallest parish church. Cosmonauts
> orbiting the earth have complained their view of Northern Europe at night
> is being blinded by the brilliant beams illuminating the Boston Stump in
> Lincolnshire.

This is an excellent story, making me to think about it.

Let us assume they have 3 kW sources producing a 5 degree cone. If just
half of the produced 0.3 Mlm would go there, the luminous intensity
would be some 25 Mcd.

At a 250 km distance, it would amount to (25e6 / 6e10 =) 4e-4 lx, or
almost -6 mag (0 mag corresponds to 2.56e-6 lx). This may be surely
annoying. Try to glimpse faint stars, or details in the Milky Way, if they
are close to Venus, which is four times fainter. Even a point source like
Venus, giving merely 1e-4 lm/m2 would be surely an obstacle for viewing
nighttime Britain. A single 1 kW luminaire could produce that 0.1 mlm/m2.

If the cone of a 1 kW beamer would be just 1 degree open, which is
possible as well, it could be visible as -7.5 mag star, spoiling the whole
view of Northern Europe indeed.

Which church is the worst one depends on the aiming of the beamers. Any
strong beamer which tries to illuminate the tip of the tower may be very
bad, if you come into its cone.

I've seen Czech landscape at night from a low-flying plane. Those
churches, which were illuminated, were mostly invisible from above --
horrible lights were apparent only. Seeing such glaring points I could
just guess, there is a church. Since the church became illuminated in such
a neglecting way, it ceased to be visible from the God's view.

Fortunately, all of those lights we flew across were just broad-cone
ones.

The choice is not
  having a lit church
 or
  saving the view of the Earth from above.
The simple solution is letting no light miss the church and
proceed upwards. The very tip of the building needs not be bathed in a
strong upward stream of light missing it from 90 per cent.

If the vicar is not an atheist, he should care about the view of the
church from the heavens as well, shouldn't he? (Not to speak about the
problem the heavens being invisible from the ground, if you stay near to
such a strongly illuminated structure. The tip of the tower points just
_nowhere_, unlike in the times it has been erected.)

good clean night,
 jenik