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 2, 16:11 -0500
On 2 Aug 2006 at 16:19, FrankReedCT@aol.com wrote:
> Is there more to it? If you hold a piece of paper up in front of the
> ocular (eyepiece) of a medium-sized backyard telescope when it is focused
> on the Sun, the paper will burst into flames within a second or two. Isn't
> that a hint of danger? On another note, a spot of very bright light on the
> retina illuminating an area 1 millimeter across may have different effects
> than light of the same brightness illuminating an area 7 millimeters
> across. To what extent have the human eye's defense mechanisms evolved to
> deal with the threat of the "normal" Sun that might not apply to a
> magnified Sun?
You can't increase the intensity of the image more than the source. So for
the sun, with a surface temperature of about 5000°C, you won't be able to
use lenses to get any better than that. Of course, that's pretty hot! [as
an aside, a curious fact is that if you pretend that animal muscles are
heat engines, then the temperature needed to get the actual efficiency is
also about 5000°C.]
The lens in your eye will only cause an increase in temperature of about
2°C on the retina, so the actual damage caused by looking at the sun with
the naked eye is photochemical. With a telescope, though, one can get much
higher temperatures on the retina. Protein denaturation (cooking) occurs
at around 60°C and it would awfully surprising if you couldn't get that
with a telescope.
> Anyway, I'm just throwing this out there for discussion. It's 98 degrees
> Fahrenheit in Chicago today, so talking about the Sun seems topical.
Yeesh! I don't know how people stand it.
Ken Muldrew.
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From: Ken Muldrew
Date: 2006 Aug 2, 16:11 -0500
On 2 Aug 2006 at 16:19, FrankReedCT@aol.com wrote:
> Is there more to it? If you hold a piece of paper up in front of the
> ocular (eyepiece) of a medium-sized backyard telescope when it is focused
> on the Sun, the paper will burst into flames within a second or two. Isn't
> that a hint of danger? On another note, a spot of very bright light on the
> retina illuminating an area 1 millimeter across may have different effects
> than light of the same brightness illuminating an area 7 millimeters
> across. To what extent have the human eye's defense mechanisms evolved to
> deal with the threat of the "normal" Sun that might not apply to a
> magnified Sun?
You can't increase the intensity of the image more than the source. So for
the sun, with a surface temperature of about 5000°C, you won't be able to
use lenses to get any better than that. Of course, that's pretty hot! [as
an aside, a curious fact is that if you pretend that animal muscles are
heat engines, then the temperature needed to get the actual efficiency is
also about 5000°C.]
The lens in your eye will only cause an increase in temperature of about
2°C on the retina, so the actual damage caused by looking at the sun with
the naked eye is photochemical. With a telescope, though, one can get much
higher temperatures on the retina. Protein denaturation (cooking) occurs
at around 60°C and it would awfully surprising if you couldn't get that
with a telescope.
> Anyway, I'm just throwing this out there for discussion. It's 98 degrees
> Fahrenheit in Chicago today, so talking about the Sun seems topical.
Yeesh! I don't know how people stand it.
Ken Muldrew.
--~--~---------~--~----~------------~-------~--~----~
To post to this group, send email to NavList@fer3.com
To , send email to NavList-@fer3.com
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