A solar eclipse occurs when the moon blocks any part of the
sun. On Monday, August 21, 2017, a solar eclipse will be visible (weather
permitting) across all of North America. The whole continent will experience a
partial eclipse lasting 2 to 3 hours. Halfway through the event, anyone within
a roughly 70-mile-wide path from Oregon to South Carolina (https://go.nasa.gov/2pC0lhe) will
experience a brief total eclipse, when the moon completely blocks the sun’s
bright face for up to 2 minutes 40 seconds, turning day into night and making
visible the otherwise hidden solar corona — the sun’s outer atmosphere — one of
nature’s most awesome sights. Bright stars and planets will become visible as
well.
Looking directly at the sun is unsafe except during the
brief total phase of a solar eclipse (“totality”), when the moon entirely
blocks the sun’s bright face, which will happen only within the narrow path of
totality (https://go.nasa.gov/2pC0lhe).
The only safe way to look directly at the uneclipsed or
partially eclipsed sun is through special-purpose solar filters, such as
“eclipse glasses” (example shown at left) or hand-held solar viewers. Homemade
filters or ordinary sunglasses, even very dark ones, are not safe for looking
at the sun. To date four manufacturers have certified that their eclipse
glasses and handheld solar viewers meet the ISO 12312-2 international standard
for such products: Rainbow Symphony, American Paper Optics, Thousand Oaks
Optical, and TSE 17.
- Always
inspect your solar filter before use; if scratched or damaged, discard it.
Read and follow any instructions printed on or packaged with the filter.
Always supervise children using solar filters.
- Stand
still and cover your eyes with your eclipse glasses or solar viewer before
looking up at the bright sun. After glancing at the sun, turn away and
remove your filter — do not remove it while looking at the sun.
- Do not
look at the uneclipsed or partially eclipsed sun through an unfiltered
camera, telescope, binoculars, or other optical device. Similarly, do not
look at the sun through a camera, a telescope, binoculars, or any other
optical device while using your eclipse glasses or hand-held solar viewer
— the concentrated solar rays will damage the filter and enter your
eye(s), causing serious injury. Seek expert advice from an astronomer
before using a solar filter with a camera, a telescope, binoculars, or any
other optical device.
- If you
are within the path of totality (https://go.nasa.gov/2pC0lhe), remove your solar filter
only when the Moon completely covers the sun’s bright face and it suddenly
gets quite dark. Experience totality, then, as soon as the bright sun
begins to reappear, replace your solar viewer to glance at the remaining
partial phases.
A solar eclipse is one of nature’s grandest spectacles. By
following these simple rules, you can safely enjoy the view and be rewarded
with memories to last a lifetime.
This document does not constitute medical advice. Readers
with questions should contact a qualified eye-care professional.
Additional Safety Information
An eclipse is a rare and striking phenomenon you won't want
to miss, but you must carefully follow safety procedures. Don't let the requisite
warnings scare you away from witnessing this singular spectacle! You can
experience the eclipse safely, but it is vital that you protect your eyes at
all times with the proper solar filters. No matter what recommended technique
you use, do not stare continuously at the sun. Take breaks and give your eyes a
rest! Do not use sunglasses: they don't offer your eyes sufficient protection.
One excellent resource for safe solar eclipse viewing is here: http://www.nasa.gov/content/eye-safety-during-a-total-solar-eclipse(link
is external)
Viewing with Protection -- Experts suggests that
one widely available filter for safe solar viewing is number 14 welder's glass.
It is imperative that the welding hood houses a #14 or darker filter. Do not
view through any welding glass if you do not know or cannot discern its shade
number. Be advised that arc welders typically use glass with a shade much less
than the necessary #14. A welding glass that permits you to see the landscape
is not safe. Inexpensive eclipse glasses have special safety filters that
appear similar to sunglasses, but these do permit safe viewing.
Telescopes with Solar Filters – Eclipses are
best viewed directly when magnified, which means a telescope with a solar
filter or solar telescopes. These will give you a magnified view that will
clearly show the progress of an eclipse. Never look through a telescope without
a solar filter on the large end of the scope. And never use small solar filters
that attach to the eyepiece (as found in some older, cheaper telescopes.)
Pinhole projectors (link is external) -- Pinhole projectors and other projection techniques are a safe, indirect viewing technique for observing an image of the sun. These provide a popular way for viewing solar eclipses.
Related projection methods -- One viewing
technique is to project an image of the sun onto a white surface with a
projecting telescope. This is explained further here: http://www.astrosociety.org/education/publications/tnl/05/stars2.html(link
is external).
The Exploratorium demonstrates how to view a planet in transit or an eclipse safely by projecting the image with binoculars: http://www.exploratorium.edu/transit/how.html(link is external). There are commercially available projection telescopes as well.
The Exploratorium demonstrates how to view a planet in transit or an eclipse safely by projecting the image with binoculars: http://www.exploratorium.edu/transit/how.html(link is external). There are commercially available projection telescopes as well.
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