Looking directly at the sun is always unsafe except during the brief total phase of a solar eclipse (totality) if you are in this particular path -- when the moon entirely blocks the sun’s bright face. This minute (or two) of totality will happen only within this narrow path. In all other areas, having solar glasses during the entire eclipse viewing is necessary.
The only safe way to look directly at the uneclipsed, or partially eclipsed, sun is through special-purpose solar filters, such as 'eclipse glasses' or hand-held solar viewers. Homemade filters or ordinary sunglasses, even those with very dark lenses, are not safe for looking at the sun - they transmit thousands of times too much sunlight.
Refer to the American Astronomical Society (AAS) Reputable Vendors of Solar Filters & Viewers page for a list of manufacturers and authorized dealers of eclipse glasses and handheld solar viewers verified to be compliant with the ISO 12312-2 international safety standard for such products. One quick way to tell if the cardboard glasses you may be able to pick up at your local store, library, or museum are reputable is to look for the ISO stamp on the inside of the glasses.
Approximately half of all libraries in the United States (in each state) have solar glasses that they are giving away for free, so check with your local library if you do not yet have a pair. The following retail chains have all been carrying solar glasses for a few dollars per pair:
- 7-Eleven
- Best Buy
- Bi-Mart
- Casey's General Store
- Circle K
- Hobby Town
- Kirklands
- Kroger
- London Drugs
- Love's Travel Stops [sold out]
- Lowe's
- Maverik
- McDonald's (Oregon only)
- Pilot/Flying J
- Toys "R" Us
- Walmart
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 injury.
Seek expert advice from an astronomer before using a solar filter with a camera, a telescope, binoculars, or any other optical device. Note that solar filters must be attached to the front of any telescope, binoculars, camera lens, or other optics.
If you are within the path of totality, 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 look at the remaining partial phases.
Outside the path of totality, you must always use a safe solar filter to view the sun directly. If you normally wear eyeglasses, keep them on. Put your eclipse glasses on over them, or hold your handheld viewer in front of them. Note: If your eclipse glasses or viewers are compliant with the ISO 12312-2 safety standard, you may look at the uneclipsed or partially eclipsed sun through them for as long as you wish. Furthermore, if the filters aren't scratched, punctured, or torn, you may reuse them indefinitely.
Some glasses/viewers are printed with warnings stating that you shouldn't look through them for more than 3 minutes at a time, and that you should discard them if they are more than 3 years old. Such warnings are outdated and do not apply to eclipse viewers compliant with the ISO 12312-2 standard adopted in 2015.
An alternative method for safe viewing of the partially eclipsed sun is pinhole projection. For example, cross the outstretched, slightly open fingers of one hand over the outstretched, slightly open fingers of the other, creating a waffle pattern. With your back to the sun, look at your hands’ shadow on the ground. The little spaces between your fingers will project a grid of small images on the ground, showing the sun as a crescent during the partial phases of the eclipse. Or just look at the shadow of a leafy tree during the partial eclipse; you'll see the ground dappled with crescent suns projected by the tiny spaces between the leaves.
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.
(inexpensive options for viewing the eclipse):
Feeling handy? Build a solar viewer yourself. Instructions: http://richardsont.people.cofc.edu/safe_solar_folder/index.html
Read more about Terry Richardson, senior instructor of astronomy and physics at the College of Charleston, who has made sure everyone can afford to safely view the eclipse: http://today.cofc.edu/2017/06/13/solar-eclipse-viewer-diy/
A sun funnel is another option for viewing the Solar Eclipse - and one that several people at once can safely observe. Instructions for building this (if you already have a telescope): https://eclipse.aas.org/sites/eclipse.aas.org/files/Build-Sun-Funnel-v3.2.pdf
Additional information:
https://eclipse2017.nasa.gov
https://eclipse.aas.org
Live video streaming of the 2017 Solar Eclipse: https://www.nasa.gov/eclipselive
For viewing through cameras, telescopes, or binoculars, using a solar filter sheet is one less expensive way to outfit your gadgets for safe viewing.
Above: cloud coverage averages along line of totality.
For updates: http://www.americaneclipse2017.org/observing-the-eclipse/weather-prospects/
For updates: http://www.americaneclipse2017.org/observing-the-eclipse/weather-prospects/
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