Louis Scheffer wrote in message ...
(Henry Spencer) writes:

In article ,
Bruce Palmer wrote:
Nevertheless, as you move away from the sun, beyond 1 AU, there must be
a point at which the intensity of harmful radiation falls below the
level that will damage your eyes.

It might be a long way out. The apparent brightness, in photons per
square degree, doesn't change with distance [...] you might be well out
of the solar system before the combined effects make the Sun eye-safe.

This seems unlikely. Laser beams can be focused to points even smaller
than the sun, and 1 mw lasers are considered almost completely safe.

This leads to a curious numerical coincidence. If you are X AU from
the sun, then you can safely view the sun through optics of size X mm
in diameter. (At 1 AU, 1 mw comes through a 1 mm circular aperature).
So if you are the distance of TAU, the mission to one thousand AU,
then you can safely view the sun through anything up to and including
a 1-meter telescope. So at that distance the sun could surely be
considered eye-safe. (And at 1 mw/m^2 irradiation, that mission will
not be using conventional solar panels. Although you could imagine a
large solar sail that doubles as a concentrator...)

Lou Scheffer