NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Looking at the Sun through a telescope
From: Ken Muldrew
Date: 2006 Aug 4, 16:38 -0500
On 4 Aug 2006 at 20:50, George Huxtable wrote:
> The only way that I can envisage heat-damage behaving in a different
> way from light-damage is that one might expect heat to diffuse away,
> more effectively, from a tiny spot into the surrounding area, than it would
> if a larger area was being heated. That wasn't an argument deployed by Ken,
> but it might have some validity, depending on the time-scales involved.
Heat removal from the eye will mostly be through the vasculature. There
are a couple of venules removing blood from the retina but they are
intertwined with the arterioles and so form something of a heat exchanger.
Thus while photochemical damage is caused by atomic level transitions (or
ionization?), heat injury does not depend on the energy density as much as
the total energy being delivered. It's possible that much of the energy
that is dumped on the retina can go into heating. I'm not sure if anyone
has a good understanding of heat transfer within the eye although the
principle worry of leaking microwave ovens is cooking the humours of the
eye so perhaps there has been work done on it.
I don't know if a sextant scope or binoculars can provide enough heat to
cause damage or not, but I would be surprised if an astronomical scope
aimed at the sun didn't cause retinal burning.
Ken Muldrew.
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From: Ken Muldrew
Date: 2006 Aug 4, 16:38 -0500
On 4 Aug 2006 at 20:50, George Huxtable wrote:
> The only way that I can envisage heat-damage behaving in a different
> way from light-damage is that one might expect heat to diffuse away,
> more effectively, from a tiny spot into the surrounding area, than it would
> if a larger area was being heated. That wasn't an argument deployed by Ken,
> but it might have some validity, depending on the time-scales involved.
Heat removal from the eye will mostly be through the vasculature. There
are a couple of venules removing blood from the retina but they are
intertwined with the arterioles and so form something of a heat exchanger.
Thus while photochemical damage is caused by atomic level transitions (or
ionization?), heat injury does not depend on the energy density as much as
the total energy being delivered. It's possible that much of the energy
that is dumped on the retina can go into heating. I'm not sure if anyone
has a good understanding of heat transfer within the eye although the
principle worry of leaking microwave ovens is cooking the humours of the
eye so perhaps there has been work done on it.
I don't know if a sextant scope or binoculars can provide enough heat to
cause damage or not, but I would be surprised if an astronomical scope
aimed at the sun didn't cause retinal burning.
Ken Muldrew.
--~--~---------~--~----~------------~-------~--~----~
To post to this group, send email to NavList@fer3.com
To , send email to NavList-@fer3.com
-~----------~----~----~----~------~----~------~--~---
