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[sci.astro] General (Astronomy Frequently Asked Questions) (2/9)
Section - B.12 Is it O.K. to look at the Sun or solar eclipses using exposed film? CDs?

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Top Document: [sci.astro] General (Astronomy Frequently Asked Questions) (2/9)
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See reader questions & answers on this topic! - Help others by sharing your knowledge
Author: Joseph Lazio <jlazio@patriot.net>,
	Steve Willner <swillner@cfa.harvard.edu>

This question appears most frequently near the time of solar eclipses.

The short answer is no!  The unobscured surface of the sun is as
bright as ever during a partial eclipse and just as capable of causing
injury.  The injured area on the retina may be a bit smaller, of
course, but that's no reason to risk damage.  Moreover, there are no
nerve endings in the retina, so one can do permanent damage without
being aware of it.

People have proposed a host of methods for viewing the Sun, including
exposed film and CDs.  These home-grown methods typically suffer from
two flaws.  First, they do not cut out enough visible light.  Second,
they provide little protection against ultraviolet or infrared light.

The only safe method for viewing the Sun directly is using No. 14
arc-welder filter or a metallicized glass or Mylar filter.  A local
hardware store or construction supply store should carry or know where
to obtain arc-welder filters.  Many astronomy magazines carry ads for
solar filters.

Whatever filter you use, inspect it to make sure it has not been
damaged.  Even a pinhole can let through enough light to cause injury.
If you use a filter over a telescope or binocular, make sure the
filter is firmly attached and cannot come off accidentally!  Never use
an eyepiece filter, which can overheat and crack.  Any filter should
cover the entire entrance aperture (or more precisely, any part of the
entrance aperture that isn't covered by something completely opaque).
If using only one side of a binocular, cover the other side.

An alternative way to view the sun is in projection.  You can use a
pinhole camera or a telescope, eyepiece, and screen.  Many observing
handbooks illustrate suitable arrangements.  This method is not only
safe, it can give a magnified image and make it easier to see details.

If you are lucky enough (or put in the advance planning) to see a
total solar eclipse, the total phase can be enjoyed with no eye
protection whatsoever.  In fact, experienced eclipse-goers often cover
one eye with a patch for several minutes before totality so the eye
will be dark-adapted during totality.  Just be sure to look away (or
through your filter again) the instant totality is over.

Additional information on the safe viewing of solar eclipses is at the
Eclipse Home Page, <URL:http://sunearth.gsfc.nasa.gov/eclipse/>.

User Contributions:

1
Keith Phemister
⚠
Sep 13, 2024 @ 11:23 pm
Copied from above: If the Universe were infinitely old, infinite in extent, and filled
with stars, then every direction you looked would eventually end on
the surface of a star, and the whole sky would be as bright as the
surface of the Sun.
Why would anyone assume this? Certainly, we have directions where we look that are dark because something that does not emit light (is not a star) is between us and the light. A close example is in our own solar system. When we look at the Sun (a star) during a solar eclipse the Moon blocks the light. When we look at the inner planets of our solar system (Mercury and Venus) as they pass between us and the Sun, do we not get the same effect, i.e. in the direction of the planet we see no light from the Sun? Those planets simply look like dark spots on the Sun.
Olbers' paradox seems to assume that only stars exist in the universe, but what about the planets? Aren't there more planets than stars, thus more obstructions to light than sources of light?
What may be more interesting is why can we see certain stars seemingly continuously. Are there no planets or other obstructions between them and us? Or is the twinkle in stars just caused by the movement of obstructions across the path of light between the stars and us? I was always told the twinkle defines a star while the steady light reflected by our planets defines a planet. Is that because the planets of our solar system don't have the obstructions between Earth and them to cause a twinkle effect?
9-14-2024 KP

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