[OT] Looking at the sun - Safe distance?

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 -- the amount of light
received by a given collector (e.g. your pupil) drops off according to the
inverse-square law, but so does the apparent area of the Sun. So the spot
of concentrated light on your retina gets smaller, but the light intensity
within it doesn't change. Eventually, second-order effects like optical
imperfections in the eye will start to blur it, and conduction cooling
will get more effective as the heated area gets smaller, but you might
be well out of the solar system before the combined effects make the Sun
eye-safe.

Indeed, the danger to your eyes may be greater in the outer solar system,
because the focused spot will still be damaging, but the total brightness
won't be high enough to trigger the argh-that's-too-damned-bright reflex
that prevents you from staring at the Sun without deliberate effort here.
--
MOST launched 30 June; science observations running | Henry Spencer
since Oct; first surprises seen; papers pending. |