What is a Solar Eclipse?
A solar eclipse is a celestial event in which the moon passes between the sun and Earth and blocks all or part of the sun for up to about three hours, from beginning to end, as viewed from a given location.
As noted by NASA, the last time most Americans experienced a total solar eclipse was 1991. In 2017, an estimated 500 million people will be able to observe the August 21, 2017 total solar eclipse, in partial or total form. For this eclipse, the longest period when the moon completely blocks the sun from any given location along the path will be about two minutes and 40 seconds.
The ONLY safe way to look directly at the uneclipsed or partially eclipsed sun is through special-purpose hand held solar filters or “eclipse-glasses." Homemade filters or ordinary sunglasses (even very dark ones) are not safe for looking at the sun.
Safe “eclipse glasses” or hand held filters must meet a very specific worldwide standard known as ISO 12312-2; this will be noted on the device. (Beware that some disreputable online vendors are selling glasses with this number on them and they are not true safe “eclipse glasses.”) You should not be able to see anything through a safe solar filter except the sun. If you can see lights of more ordinary brightness through your eclipse glasses or handheld viewer and you are not sure if the product came from a reputable vendor, it is no good. A list of reputable vendors and more information on viewing the eclipse can be found on the American Astronomical Society website.
A few rules of thumb to keep in mind when buying and using solar eclipse glasses are noted below:
- Thoroughly inspect your solar filter glasses; if they are scratched, creased, punctured, torn or otherwise damaged discard them and do not use that pair.
- Put the solar filter glasses over your normal eyeglasses if you wear glasses.
- Always supervise children using solar filters.
- After looking at the sun, turn your head away from the sun before you remove your solar filter glasses.
Eclipse Viewing Through a Camera
Although it may seem safe, you should not ever look at the partially eclipsed sun through an unfiltered camera, telescope, binoculars, cellphone or any other optical device. In addition, doing so through a solar filter could be an even worse activity, as the concentrated solar rays could damage the filter and enter your eyes, causing serious injury.
If you plan on using a solar filter with a camera, telescope, binoculars or any other optical device you should seek expert advice from an astronomer before doing this – the appropriate filters need to be attached to the front of any optical device.
The Path of Totality
You may have heard the phrase "path of totality" when referencing this year's eclipse viewing. Anyone within the path of totality can see one of nature’s most awe-inspiring sights - a total solar eclipse. This path, where the moon will completely cover the sun and the sun's tenuous atmosphere - the corona - can be seen, will stretch from Lincoln Beach, Oregon to Charleston, South Carolina.
If you are fortunate enough to be in the path of totality, you can only safely remove your solar filter when the moon completely covers the sun’s bright face and it suddenly gets quite dark. As soon as the bright sun begins to reappear, replace your solar viewer. Outside of the path of totality, you must always use a solar filter to view the sun.
Watching a solar eclipse without appropriate protection can seriously damage your retina permanently and even cause blindness called solar retinopathy. The only safe way to watch a solar eclipse is with the above mentioned solar filters known as “eclipse glasses” or in hand held solar filters that meet the worldwide standard known as ISO 12312-2. Stay safe and enjoy one of nature's greatest shows!
If you have further questions about viewing the eclipse, or anything related to your eyesight, contact Donna Maxfield, MD, FAAO, an Ophthalmologist with the LewisGale Physicians team at (540) 265-1624, or book an appointment online via the button below.