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On 12 May 2004 at 17:10, Ken Muldrew wrote:

> I have a recollection, and I'll try to find the reference tonight,
> that viewing the sun with the naked eye only results in photochemical
> injury to the retina, not a heat-related burn. But I may be
> misremembering.

The article that I recalled was an editorial in Ophthalmic
Physiological Optics (21: 427-429, 2001). They cite a calculation
that shows naked eye heating from the sun at about 2?C; not enough to
cause injury. Their view is that any method that allows the non-
eclipsed sun to be looked at comfortably will probably not cause any
damage (e.g. Socrates' suggestion of looking at the reflection of the
sun in water is almost OK (add some sunglasses and it may be fine),
and any filter that provides an optical density of 5 or more will
protect the retina; even if it's smoked glass (as long as the soot is
uniform!)). The damaging wavelengths are supposed to be blue and near
uv by these authors.

> typical sextant scopes) then Liouville's theorem tells us that there

In another post George asked for an explicit statement of Liouville's
theorem. It is just the theorem from statistical mechanics that
states that volume in phase space is conserved. It applies equally to
particles and waves with the further restriction on the upper limit
of phase space density with waves.

Ken Muldrew.

   

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