[OT] Looking at the sun - Safe distance?

OT, I know, but I couldn't find what looked like an appropriate newsgroup...

We know looking directly at the sun will damage the human eye. What
about on Mars? Jupiter? More generally, what is the threshold distance
beyond which it would be considered "safe" to look at the sun? I guess
this is a Poynting vector/physiology type question. Searching the web
just adds to the confusion. Is the distance close enough to still
resolve the sun's disk or so far away that it appears as only a point
light source?

On some afternoons, depending on clouds and atmospheric dust, the sun
looks like a giant orange ball that you can actually look at without eye
damage as it sets, but I've no idea what attenuation of its intensity
that translates into.

--
bp
Proud Member of the Human O-Ring Society Since 2003

In article , Bruce Palmer wrote:

On some afternoons, depending on clouds and atmospheric dust, the sun
looks like a giant orange ball that you can actually look at without eye
damage as it sets,

I saw an annular eclipse, just on the point where it rose above the
horizon as it left "totality" (okay, maxima, YKWIM). Got about maybe
five degrees up, then we could see a sliver... thick morning mist...
which meant we could sit and watch the sun, no protective equipment or
any form of discomfort, for the best part of half an hour as the moon
slipped in front of it. Remarkable.

These clear-sky eclipses don't have *all* the tricks :-)

--
-Andrew Gray

In article ,
Bruce Palmer wrote:
On some afternoons, depending on clouds and atmospheric dust, the sun
looks like a giant orange ball that you can actually look at without eye
damage as it sets...

A note of caution: safely low visible-light intensity doesn't necessarily
equate to safely low UV and IR intensity (especially the latter, which has
a tendency to penetrate clouds etc. better than visible light). Your eye
is not a reliable guide to what's eye-safe.

(I'll admit to having yielded to the temptation to look in such situations,
especially when there were naked-eye sunspot groups visible... but only in
brief glances, never looking steadily.)
--
MOST launched 30 June; science observations running | Henry Spencer
since Oct; first surprises seen; papers pending. |

"Henry Spencer" wrote in message
...
In article ,
Bruce Palmer wrote:
On some afternoons, depending on clouds and atmospheric dust, the sun
looks like a giant orange ball that you can actually look at without eye
damage as it sets...

A note of caution: safely low visible-light intensity doesn't necessarily
equate to safely low UV and IR intensity (especially the latter, which has
a tendency to penetrate clouds etc. better than visible light). Your eye
is not a reliable guide to what's eye-safe.

This is in fact my understanding of exactly why total eclipses are so
dangerous. You're not expecting the still high UV/IR does and your pupils
are more dilated than usual, allowing more light in.


(I'll admit to having yielded to the temptation to look in such
situations,
especially when there were naked-eye sunspot groups visible... but only in
brief glances, never looking steadily.)

So, build a shadow box. An old shoe-box works great. I keep mine around
for eclipses. Should scale it up so I can watch sunspots.


--
MOST launched 30 June; science observations running | Henry Spencer
since Oct; first surprises seen; papers pending. |

"Greg D. Moore (Strider)" wrote in message
...

"Henry Spencer" wrote in message
...
In article ,
Bruce Palmer wrote:
On some afternoons, depending on clouds and atmospheric dust, the sun
looks like a giant orange ball that you can actually look at without
eye
damage as it sets...

A note of caution: safely low visible-light intensity doesn't
necessarily
equate to safely low UV and IR intensity (especially the latter, which
has
a tendency to penetrate clouds etc. better than visible light). Your
eye
is not a reliable guide to what's eye-safe.

This is in fact my understanding of exactly why total eclipses are so
dangerous. You're not expecting the still high UV/IR does and your pupils
are more dilated than usual, allowing more light in.


(I'll admit to having yielded to the temptation to look in such
situations,
especially when there were naked-eye sunspot groups visible... but only
in
brief glances, never looking steadily.)

So, build a shadow box. An old shoe-box works great. I keep mine around
for eclipses. Should scale it up so I can watch sunspots.

I used a colander from the kitchen, and I got dozens of little crescents on
the wall last time (4-12-2002)

I was reading in the bathroom when I ran across an item written by
"Greg D. Moore \(Strider\)" on Mon, 05 Jan 2004
04:41:22 GMT, which said:

So, build a shadow box. An old shoe-box works great. I keep mine around
for eclipses. Should scale it up so I can watch sunspots.

For a few bucks you can get a mylar-like sheet of Baader Solar Filter
material. I used some to make a filter for my telescope and looked at
the sun directly, rather than by projection. Had to give it up,
though, since the telescope was a reflector and I was getting
sunburned over only the left side of my face.


-------------
Beady's 11th Law of Social Harmonics: "Your spouse is precisely the kind of person someone like you would choose to marry."

"John Beaderstadt" wrote in message
...
I was getting
sunburned over only the left side of my face.

That happened to me once, but it was after a champagne breakfast at uni.

In article ,
Greg D. Moore \(Strider\) wrote:
A note of caution: safely low visible-light intensity doesn't necessarily
equate to safely low UV and IR intensity (especially the latter...

This is in fact my understanding of exactly why total eclipses are so
dangerous. You're not expecting the still high UV/IR does and your pupils
are more dilated than usual, allowing more light in.

If memory serves, total eclipses are safe for naked-eye viewing *during*
*totality*. But caution has to be exercised during the partial phases
before and after totality.
--
MOST launched 30 June; science observations running | Henry Spencer
since Oct; first surprises seen; papers pending. |

On Mon, 5 Jan 2004, Neil Gerace wrote:

I used a colander from the kitchen, and I got dozens of little crescents on
the wall last time (4-12-2002)

Next time, try saltines as well.

The only optical imaging system you can eat after the eclipse is over.

--
Bill Higgins | They can have my World Almanac
Fermilab | when they pry it from my cold, dead fingers.
Internet: | Or when next year's edition comes out, whichever is first.
| --Lois A. Fundis

Henry Spencer wrote:

In article ,
Bruce Palmer wrote:

On some afternoons, depending on clouds and atmospheric dust, the sun
looks like a giant orange ball that you can actually look at without eye
damage as it sets...


A note of caution: safely low visible-light intensity doesn't necessarily
equate to safely low UV and IR intensity (especially the latter, which has
a tendency to penetrate clouds etc. better than visible light). Your eye
is not a reliable guide to what's eye-safe.

(I'll admit to having yielded to the temptation to look in such situations,
especially when there were naked-eye sunspot groups visible... but only in
brief glances, never looking steadily.)

Interesting. I hadn't thought of that. Luckily I can't ever
remembering actually staring at it that way for more than a short while.

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. I'm going to try to find an
ophthamologist (sp?) who might be able to tell me the level of radiation
(at whatever wavelength) considered "safe". From there it should be
simple to derive a distance from the sun. I realize that the "safe"
distance in an ocular sense might not be "safe" in terms of other
energized particles that could cause radiation damage of other sorts.

I was watching a hockey game the other night and one of the opposing
team members' last name was Van Allen. At one point I yelled at the TV
"How's your radiation belt?" and got the most peculiar glance from my
wife. She sort of laughed. I thought it was funny. Guess you had to
be there.

--
bp
Proud Member of the Human O-Ring Society Since 2003