| National Geographic | - |
Soak
up these safety tips for skywatchers wanting to take in the beauty of a
solar eclipse. Photo of people watching solar eclipse in Rebun Island,
Japan in 1949.
How to Safely Watch a Solar Eclipse
Soak up these safety tips for skywatchers wanting to take in the beauty of a solar eclipse.
Be careful—don't look directly at the sky during this weekend's rare hybrid eclipse.
Photograph by Maynard Owen Williams, National Geographic
Published November 2, 2013
We've all heard the warnings before:
Looking directly at the sun, whether it's with your naked eyes or
through an optical aid, can be extremely dangerous.
This
holds true on any regular sunny day—and when there is a partial solar
eclipse. However, there are easy, safe ways to soak in the sun’s great
disappearing act.
For the
fleeting few minutes during a total eclipse when the entire disk of the
sun is completely covered by the moon’s silhouette, it is completely
safe to look directly at it with your naked eyes.
However,
during an annular ("ring of fire") eclipse or a partial eclipse—where
only a portion or even a tiny bite appears to be taken out of the solar
disk—it is always extremely dangerous to look at the sun directly.
While viewing a total eclipse is safe, it’s important to be aware of when it ends and when the sun starts its return.
Don't Stare at the Sun
Even
if only a tiny sliver of the sun can be seen, it's too bright for our
eyes. Less than 1 percent of the visible sun is still 4,000 times
brighter than the full moon.
The
retina of an unprotected eye can burn in as little as 30 seconds. It is
particularly dangerous to use binoculars or a telescope to look at the
sun. A retinal burn in that case can be frighteningly fast—taking no
more than a fraction of a second.
And
what makes it even more scary is that because the retina of the eye
lacks pain receptors, you won't feel it happening. And the effects may
not appear until hours after the damage has been done.
Use Approved Filters
Many
materials and methods popularly used to observe an eclipse may be
unsafe. Smoked glass, x-ray films, sunglasses, and camera filters, for
example, are all dangerous and should be avoided completely.
That's
because while they reduce the incoming visible light, they fail to stop
the full force of the sun's hazardous infrared and ultraviolet
radiation.
Despite the warnings, there are plenty of ways to safely enjoy one of Mother Nature’s most amazing spectacles.
Mylar Filters
Major
telescope manufacturers sell aluminum-coated mylar plastic sheets that
are available as eclipse viewing glasses or as ring filters that fit
over the front of telescopes. These coated filters render the sun in
steely blue-white color.
Forget
about using those Mylar space blankets sold at camping stores; they are
way too thin and flimsy, letting in dangerous amounts of strong light.
Welders Glass
For
those with more experience with solar viewing who want to catch the
partial phases of an eclipse, a number 14 arc welder’s glass can work
well. The rectangular piece of dark green glass filters out all
ultraviolet and infrared radiation and reduces visible light by a factor
of at least 300,000.
The only problem with this method is finding a handy local welder’s supply store when you need it.
Telescope Glass Filters
The
best way to see the eclipse unfold up-close is by using metal-on-glass
filters that fit on the front end of binoculars and telescopes.
Commonly
available at local and online astronomy stores, these filters provide a
safe, pleasing orange-yellow hue and are great to use for photography
and sunspot viewing as well.
Pinhole Projection
By
far the safest method of watching the sun anytime, even during an
eclipse, is to avoid gazing at the spectacle directly at all but instead
look at a projected image of the sun. A simple pinhole camera can do
the trick.
To make one, poke a
three-millimeter-wide (or thereabouts) pinhole into a square piece of
cardboard paper. Then, with the sun behind you, project the sun through
that hole onto another white piece of paper. Now you can safely view the
projected image of the sun on that second piece of paper.
Remember never to look through the pinhole directly at the sun.
Notes for Astronomers
While
it is possible to project an image of the sun through telescope optics
onto a paper, it can damage your instrument. The sunlight can heat up
optics in just a few minutes, damaging eyepiece coatings and even
melting the cement that holds eyepiece optics together.
Also
avoid so-called solar eyepieces that may come with less expensive
telescopes. They are highly dangerous, as intense heat from incoming
unfiltered sunlight can hit the eyepiece and cause the lens to crack,
allowing the magnified sunlight to hit your eye.
end quote from:
No comments:
Post a Comment