Please for the interest of the masses who will love to view today's
sunday (Nov. 3, 2013) eclipse, it is advice to use welder's No 13 and No
14 glasses for avoidance of permanent blindness.
The Sun can be
viewed safely with the Unclad eye only during the few brief seconds or
minutes of a total solar eclipse. Partial eclipses, annular eclipses,
and the partial phases of total eclipses are never safe to watch without
taking special precautions. Even when 99% of the Sun's surface is
obscured during the partial phases of a total eclipse, the remaining
photospheric crescent is intensely bright and cannot be viewed safely
without eye protection [Chou, 1981; Marsh, 1982]. Do not attempt to
observe the partial or annular phases of any eclipse with the Unclad
eye. Failure to use appropriate filtration may result in permanent eye
damage or blindness!
Generally, the same equipment, techniques and precautions used to
observe the Sun outside of eclipse are required for annular eclipses and
the partial phases of total eclipses [Reynolds & Sweetsir, 1995;
Pasachoff & Covington, 1993; Pasachoff & Menzel, 1992; Sherrod,
1981]. The safest and most inexpensive of these methods is by
projection, in which a pinhole or small opening is used to cast the
image of the Sun on a screen placed a half-meter or more beyond the
opening. Projected images of the Sun may even be seen on the ground in
the small openings created by interlacing fingers, or in the dappled
sunlight beneath a leafy tree. Binoculars can also be used to project a
magnified image of the Sun on a white card, but you must avoid the
temptation of using these instruments for direct viewing.
The Sun
can be viewed directly only when using filters specifically designed
for this purpose. Such filters usually have a thin layer of aluminum,
chromium or silver deposited on their surfaces that attenuates
ultraviolet, visible, and infrared energy. One of the most widely
available filters for safe solar viewing is a number 14 welder's glass,
available through welding supply outlets. More recently, aluminized
mylar has become a popular, inexpensive alternative. Mylar can easily be
cut with scissors and adapted to any kind of box or viewing device. A
number of sources for solar filters are listed below. No filter is safe
to use with any optical device (i.e. - telescope, binoculars, etc.)
unless it has been specifically designed for that purpose. Experienced
amateur and professional astronomers may also use one or two layers of
completely exposed and fully developed black-and-white film, provided
the film contains a silver emulsion. Since all developed color films
lack silver, they are always unsafe for use in solar viewing.
Unsafe
filters include color film, some non-silver black and white film,
medical x-ray films with images on them, smoked glass, photographic
neutral density filters and polarizing filters. Solar filters designed
to thread into eyepieces which are often sold with inexpensive
telescopes are also dangerous. They should not be used for viewing the
Sun at any time since they often crack from overheating. Do not
experiment with other filters unless you are certain that they are safe.
Damage to the eyes comes predominantly from invisible infrared
wavelengths. The fact that the Sun appears dark in a filter or that you
feel no discomfort does not guarantee that your eyes are safe. Avoid all
unnecessary risks. Your local planetarium or amateur astronomy club is a
good source for additional information.
In spite of these
precautions, the total phase of an eclipse can and should be viewed
without any filters whatsoever. The Unclad eye view of totality is
completely safe and is overwhelmingly awe-inspiring!
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