Eclipses through the Centuries - Portal do Professor

joyful experience could become a real nightmare. Here you will learn how to
proceed to safely observe a solar eclipse.
Staring at the Sun without proper protection can cause irreparable damage to
the eye and is not recommendable. The Sun is a source of electromagnetic
radiation: solar X-ray, gamma ray, microwave, radio wave, ultraviolet, and
visible light. 27 When the retina is exposed to intense visible light, two kinds
of eye damage can occur, alone or simultaneously - retinal burns and thermal
injury, the latter occur without any feeling of pain, but that can cause irreparable
damage to the eye or even blindness. 28
So how can we safely observe the Sun? There are several safe methods, but
the best one is indirect projection (See “Observing Eclipses Safely,” at
http://www.mreclipse.com/Totality/TotalityCh11.html). This can be done by
projecting the Sun’s image on a white piece of paper using a pair of binoculars
(with one of the lenses covered), or by putting a small hole (about 1 mm in
diameter) in a piece of aluminum foil taped over a paper towel tube, often
called a pinhole camera. It allows safe viewing of the Sun’s projected image.
However, care must be taken to ensure that no one looks through the projector
directly, especially if children and teenagers are present, because this would
cause severe eye damage.
The Sun can be also observed with appropriate filters to block its harmful
radiation. Other improvised methods, such as looking at a reflection on water,
or looking through a compact disk, are also dangerous. Only properly designed
and certified solar filters should be used for direct viewing of the Sun, and these
must be in perfect condition, as even a small defect could cause irreparable
damage to the eye.
Please be aware that standard or polaroid sunglasses are not solar filters.
Although they may afford some eye relief if one is outside on a bright day, you
should never use them to observe the Sun. You cannot use sunglasses, even
crossed polaroids, to stare at the sun during partial phases of an eclipse. They
provide essentially no eye protection for this purpose. 29
Strictly speaking, it is safe to observe the total phase of a solar eclipse when the
Sun’s photosphere is completely covered by the Moon. The Sun’s corona will
be visible, as will be the chromosphere, solar prominences, and possibly even
solar flares. Nevertheless, even under these conditions, there is great danger in
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