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Note: I had asked this on Physics, but it is off-topic there due to being about safety.
On the BBC's guide to eclipse-watching, Dr Lucie Green says:
Watching an eclipse with normal sunglasses provides virtually no protection. In fact, they trick your eyes to let in more light, so they can cause even more damage.
This doesn't seem right, because proper sunglasses should block UV to a safer level. Surely wearing proper sunglasses at any time is safer than not? Whilst I can understand staring at the sun with sunglasses on still allows too much UV in, why couldn't someone just glance at the eclipse from time to time?
Your eyes can dilate behind sunglasses, especially when the main source of light (the sun) is blocked, and ambient light decreases. Regular sunglasses offer some protection against certain UV wavelengths, but not enough to protect your eyes when looking directly at the sun (or, during an eclipse, the corona). Most sunglasses are mainly designed to, first and foremost, look good. After that, there is some protection against UVA (400-315 nm) and UVB (280-315 nm) light. Some sunglasses also offer "UV400" protection, which is short-wavelength blue light longer than 400 nm. Polarized sunglasses do not protect against UV at all, only reflected light (such as shining off the water or from an automobile's body or glass) and glare. Different sunglasses tints (or colors) also do not protect against UV, but they can affect color perception.
Surely wearing proper sunglasses at any time is safer than not?
That is true, it is safer, the question is to what degree? Sunglasses offer some protection from indirect UV and visible light that has been scattered by the atmosphere and reflected off of things around us. However, the number and energy of photons (the "particles" of light) reaching your eyes when looking directly at the sun is dramatically greater, and so much more dangerous. Eyes can be damaged quite quickly by high-energy light of many wavelengths, including UV and visible, with the magnitude of the damage correlating to the energy of the light. Damage is also cumulative, accruing over a lifetime. Even small peeks directly at the sun will contribute to your overall lifetime risk of eye damage, and may cause permanent, irreversible harm very quickly.
There are a number of much safer alternatives for watching solar eclipses, including pinhole projectors, welding goggles rated higher than 14, various solar filters for cameras, telescopes, and binoculars, and fully exposed and developed black-and-white film (good luck finding that nowadays), among others.
Above all, make sure you're safe, and if you have any doubts consult with an expert, such as a science/natural history museum or local university's astronomy department.
How To See The 'Ring Of Fire' Today
The moon appears to cover the sun during an annular eclipse of the sun in May 2012, as seen from Chaco Culture National Historical Park in Nageezi, N.M.
Stan Honda/AFP via Getty Images
Early risers across the Northern Hemisphere may see what looks like a "ring of fire" in the sky Thursday morning as the moon passes between the Earth and the sun.
The solar eclipse, expected around sunrise, will appear that way because the moon is at or near the most distant point in its elliptical orbit around the Earth right now, so when it passes between us and our nearest star it will block out just part of the sun. A total solar eclipse happens when the moon covers up the entire sun so that only a haze of light around the darkened moon is visible.
See The Stunning Photos Of This Morning's 'Ring Of Fire' Solar Eclipse
Instead, we humans will catch one of two sights Thursday morning:
Annular solar eclipse: This is when the moon is at its farthest point from the Earth and appears very small. The whole moon passes in front of the sun, creating what looks like a doughnut hole in the middle of the star.
Partial solar eclipse: This occurs when the three celestial bodies are not perfectly lined up, so only part of the moon passes in front of the sun. In this case, the sun will look like it's had a bite taken out of it.
Only some people will be able to see an annular solar eclipse on Thursday.
But even a partial eclipse will still appear as if "the 'Death Star' is in front of the sun as it's rising," Jackie Faherty, an astrophysicist at the American Museum of Natural History in New York City, told Space.com.
Where the eclipse can be seen
According to NASA, viewers in the Southeast, Northeast and Midwestern continental United States as well as in northern Alaska will be able to see a partial eclipse before, during and just after sunrise.
A partial eclipse will also be visible in much of Canada as well as parts of Europe, Asia, northern Africa and the Caribbean.
NASA Spacecraft Made A Flyby Visit To The Largest Moon In The Solar System
People in parts of Canada, Greenland and northern Russia will be able to see the annular eclipse, the agency said.
If you're unable to see the eclipse from where you are or simply want a clearer picture, NASA is streaming the astronomical event here and here.
The stream, which begins at 5 a.m. ET, even though sunrise won't start until around 5:47 a.m., will show a partial solar eclipse.
How to gaze at the sun safely
What you heard as a child is true: It is not safe to look directly into the sun, even if it is partly covered by the moon.
That's why NASA recommends wearing "solar viewing or eclipse glasses" throughout the entire crossing. Regular sunglasses don't count.
There are also some creative alternatives to seeing the solar eclipse without risking injury to your eyes, such as viewing it through a pinhole projector or constructing a do-it-yourself wooden solar viewer.
Didn't we just have an eclipse?
Yes! But that was a bit different.
You might be thinking of the Super Flower Blood Moon lunar eclipse that occurred in late May.
The Earth passed directly between the sun and the moon, giving the moon a deep red hue in some parts of the world.
American Conference of Governmental Industrial Hygienists, "Threshold Limit Values for Chemical Substances and Physical Agents and Biological Exposure Indices," ACGIH, Cincinnati, 1996, p.100.
Chou, B. R., "Safe Solar Filters," Sky and Telescope , August 1981, p. 119.
Chou, B. R., "Eye safety during solar eclipses - myths and realities," in Z. Madourian & M. Stavinschi (eds.) Theoretical and Observational Problems Related to Solar Eclipses, Proceedings of a NATO Advanced Research Workshop . Kluwer Academic Publishers, Dordrecht, 1996 (in press).
Chou, B. R. and Krailo M. D., "Eye injuries in Canada following the total solar eclipse of 26 February 1979," Can. J. Optometry , 1981, 43(1):40.
Del Priore, L. V., "Eye damage from a solar eclipse" in M. Littman and K. Willcox, Totality: Eclipses of the Sun , University of Hawaii Press, Honolulu, 1991, p. 130.
Marsh, J. C. D., "Observing the Sun in Safety," J. Brit. Ast. Assoc. , 1982, 92, 6.
Pasachoff, J. M., and Covington, M., Cambridge Guide to Eclipse Photography , Cambridge University Press, Cambridge and New York, 1993.
Pasachoff, J. M., "Solar Eclipses and Public Education," International Astronomical Union Colloquium #162: New Trends in Teaching Astronomy , D. McNally, ed., London 1997, in press.
Penner, R. and McNair, J. N., "Eclipse blindness - Report of an epidemic in the military population of Hawaii," Am. J. Ophthalmology , 1966, 61:1452.
Pitts D. G., "Ocular effects of radiant energy," in D. G. Pitts & R. N. Kleinstein (eds.) Environmental Vision: Interactions of the Eye, Vision and the Environment , Butterworth-Heinemann, Toronto, 1993, p. 151.
Reynolds, M. D. and Sweetsir, R. A., Observe Eclipses , Astronomical League, Washington, DC, 1995.
Sherrod, P. C., A Complete Manual of Amateur Astronomy , Prentice-Hall, 1981.
Solar Eclipse 2021: Here are 7 dos and don’ts we should follow during 'Surya Grahan'
The solar eclipse this year will be visible today, June 10, 2021. However, according to NASA, this will not be visible to all, and only some parts of the globe can witness it. The annular solar eclipse appears when the Moon passes between the Earth and the Sun.
In India, the solar eclipse will only be visible from Ladakh and Arunachal Pradesh, where they can see a partial solar eclipse from 12:25 pm to 12:51 pm. This solar eclipse is a partial solar eclipse where we can see a fire ring in the sky. This means that the Moon can only cover the Sun to an extent and the rest of the uncovered Sun makes the eclipse appear like a ring of fire.
The sunlight gets restricted partially, so the sky goes dark during the peak of the eclipse. However, to err to the side of safety, here are a few directions you need to follow during the solar eclipse.
Making a judgment call
So it’s okay to look at the Sun when it's on the horizon? Well, possibly. The science is clear, but there is a caveat that on a perfectly clear, beautiful, haze-free, low humidity day even the rising Sun is going to be to be too bright to look at. It’s the conditions that make it safe, or not safe, and that’s something that requires a judgement call. The Sun needs to look deep red and not very bright, and if it's anything other than that—if there’s any sign of yellow light—it’s definitely going to be too bright to look at without solar eclipse glasses/solar filters.
“If you follow the rule to always wear ISO-rated solar filters to the letter then the worst thing that’s going to happen is that you may not see the Sun as it’s rising over the ocean,” said Dr. Rick Fienberg, Press Officer of the American Astronomical Society (AAS) and renowned eclipse-chaser. “But within a few minutes, once it gets a few degrees up, you’ll see it,” he added.
What looking at the solar eclipse without glasses could do to your eyes
Let’s get this out of the way: you absolutely cannot safely watch the solar eclipse without wearing protective glasses.
If you aren’t wearing protective glasses, ultraviolet light from the sun can penetrate and be absorbed into your retina, where it can cause a condition that eye doctors call solar retinopathy.
Most people are aware of that, but there are still some myths out there about what exactly happens to people who have looked at an eclipse without protection.
Contrary to what some warnings make it sound like, solar retinopathy doesn’t necessarily leave sufferers totally blind. For most people, the damage affects central vision and may make it blurry or spotty. In some cases, that damage goes away after a few days, weeks, or months. But in others, that damage is permanent.
And it’s all due to the power of the sun and the way an eclipse can cloud our judgment.
The sun is powerful enough that direct exposure to its light can damage your eyes or damage your camera sensor if you point a zoom lens directly at it.
Most of the time, we instinctively don’t let ourselves look at the sun — the brightness causes us to blink or look away, which is why solar retinopathy cases are mostly associated with eclipse events (other cases have occurred when people have engaged in sun-gazing rituals or when people tripping on LSD have been captivated by the sun’s brilliance).
During an eclipse when the sun isn’t totally covered by the moon, our star’s brightness decreases significantly. All of a sudden it’s not painful to look at the sun, either because the brightness has lessened so much or because our fascination overrides our pain reflex.
Either way, that decrease is deceptive. The sun is still emitting enough ultraviolet light that it could potentially damage your eyes within seconds.
“We were just doing it for a short time,” 70-year-old Lou Tomososki told Today of himself and a friend sneaking a peek at a 1962 eclipse in Oregon. “I have a little blind spot in the center of my right eye.”
That doesn’t mean everyone who has ever glanced at an eclipse has lost their vision. Solar retinopathy is difficult to predict. Ophthalmologists and optometrists reliably expect to see a few cases of it after an eclipse, according to Medscape.
Usually, people whose eyes are damaged notice a change within a few hours or by the next day (though it’s worth pointing out that cumulative damage by ultraviolet light over your lifetime can later result in eye problems).
According to NASA, symptoms usually include blurred vision, dark or yellow spots, pain, or loss of vision in the center of the eye. That sort of damage can make it hard or impossible to read or to focus on whatever is right in the center of your view.
For some people, vision recovers within 24 hours — those ones are lucky, though again, it doesn’t mean there isn’t damage to the eye, they could still see later problems. In general, people recover as much as they are going to within six months of the event, according to the American Academy of Ophthalmology.
If you are within the 70-mile-wide band of totality, you can safely remove your protective glasses once the sun is totally covered. You’ll know it’s time because you won’t be able to see anything with those glasses on. But as soon as beads of light start to re-appear, it’s time to protect your eyes again. Even 1% of the sun is enough to cause damage.
If you can’t find eclipse glasses, we’d recommend making a simple pinhole viewer to watch safely.
Eyes to the sky for Thursday morning's sunrise solar eclipse
Look to the eastern sky as the Sun rises Thursday morning. Be sure to be wearing your eclipse glasses at the time, however, so that you can take in the fantastic sight of the Moon passing in front of the Sun.
The last major astronomical event for Spring 2021 is the June 10 annular solar eclipse. As the Sun, Moon, and Earth line up for this event, the Moon's shadow will sweep across Earth's surface. It will follow a path that starts in Northern Ontario, passes across Nunavut and the Arctic Ocean to end in Siberia.
The unusual path of this eclipse is not the only thing that sets it apart. Because the Moon is near its farthest distance from Earth during the event, even at maximum, at the point of greatest eclipse, it will not completely block the Sun in a total solar eclipse. Instead, the Moon's disk will leave a 'ring of fire' around it, as it covers most of the Sun. This is known as an annular solar eclipse.
However, for most people watching, including nearly all from Canada, they will see this as only a partial eclipse.
This image of the June 21, 2020 solar eclipse shows the partial phase of the eclipse. Credit: Hong Kong Space Museum
In Canada, the eclipse will be visible either at dawn or in the hours just after sunrise, but only for viewers in the northern and eastern parts of the country. For the rest of the nation, the eclipse starts and ends before the Sun even peeks above the horizon.
With the path of totality being so remote, most viewers will only part of the Sun covered by the Moon. For this reason, anyone watching the eclipse should wear some kind of protection over their eyes (perhaps the same mylar eclipse glasses you used in August 2017?). Alternatively, a pinhole camera will allow safe viewing of the eclipse. For this annular eclipse, these precautions apply even for those watching from the path of totality.
WILL SKIES BE CLEAR??
Weather is an essential factor that will influence everyone's chances of seeing this event. Even those positioned in the most advantageous location will have their view spoiled by cloudy skies. So, be sure to check your forecast to ensure that you'll have clear enough skies to see this spectacular sight.
If your skies are clouded over, but you still want to get up and watch it live, check out the available live streams.
Watch below: TimeandDate.com's live stream begins at 5 a.m. EDT on Thursday morning.
If getting up that early is not enticing (or even possible), many of the live streams will be replayable later in the day. Plus, there's sure to be plenty of views of the eclipse on social media.
WHO WILL SEE IT??
The entire eclipse, from start to finish, will take just over two hours. How much of the eclipse you see and what part of the eclipse you see will depend on where you are watching.
The map below plots what the eclipse will look like for various locations across eastern and northern Canada, along with what time the eclipse peaks at that location.
For those in Atlantic Canada, the eclipse begins after sunrise. Other than in the far north, this region of the country offers the best view of the entire event.
St John's: sunrise 5:03 a.m. NDT, eclipse 6:05-8:10 a.m., peaks at 7:05 a.m.
Charlottetown: sunrise 5:20 a.m. ADT, eclipse 5:37-7:38 a.m., peaks at 6:35 a.m.
Halifax: sunrise 5:28 a.m. ADT, eclipse 5:36-7:35 a.m., peaks at 6:33 a.m.
Labrador City: sunrise 5:02 ADT, eclipse 5:48-7:51 a.m., peaks at 6:48 a.m.
Nain: sunrise 4:34 ADT, eclipse 5:46-7:52 a.m., peaks at 6:47 a.m.
Viewers in Quebec and Ontario will see the eclipse starting right at sunrise. In the southern regions of these provinces, the farther west the viewer is, the further along the eclipse will be at that time. Note the timing: if the starting time of the eclipse matches the timing of sunrise, the eclipse is already in progress as the Sun begins to rise.
Monteal: sunrise 5:05 a.m. EDT, eclipse 5:05-6:39 a.m., peaks at 5:39 a.m.
Ottawa: sunrise 5:14 a.m. EDT, eclipse 5:14-6:39 a.m., peaks at 5:40 a.m.
Toronto: sunrise 5:35 a.m. EDT, eclipse 5:35-6:46 a.m., peaks at 5:40 a.m.
The farther north one is in Quebec and Ontario, and thus closer to the path of totality, the earlier the Sun will rise. This will offer a better and longer view of the eclipse.
Timmins: sunrise 5:23 a.m. EDT, eclipse 5:23-6:46 a.m., peaks at 5:47 a.m.
Moosonee: sunrise 5:07 a.m. EDT, eclipse 5:40-6:51 a.m., peaks at 5:51 a.m.
Peawanuck: sunrise 5:03 a.m. EDT, eclipse 5:03-6:58 a.m., peaks at 5:59 a.m.
Skywatchers from Timmins and Moosonee will see some of the greatest partial eclipse views of the event. Meanwhile, Peawanuck, from within the path of totality, will see the complete 'ring of fire' eclipse.
Far western Ontario and southern Manitoba are special cases during this event. The Sun begins rising only four minutes before the eclipse reaches its maximum for those regions of the country. Thus, viewers will likely miss the maximum and only see the second half of the eclipse.
Thunder Bay: sunrise 5:55 a.m. EDT, eclipse 5:55-6:49 a.m., peaks at 5:59 a.m.
Winnipeg: sunrise 5:20 a.m. CDT, eclipse 5:20-5:55 a.m., peaks at 5:24 a.m.
Those farther west will not see the eclipse because it will have ended before the Sun begins to rise. However, communities farther north will still see it due to the unusual path the shadow is taking during this eclipse.
Thompson: sunrise 4:48 a.m. CDT, eclipse 4:48-6:04 a.m., peaks at 5:07 a.m.
Arviat: sunrise 3:41 a.m. CDT, eclipse 4:15-6:11 a.m., peaks at 5:12 a.m.
Yellowknife: sunrise 3:44 a.m. MDT, eclipse 3:44-5:22 a.m., peaks at 4:25 a.m.
The best view from Canada will likely be in Iqaluit and farther north.
Iqaluit: sunrise 2:18 a.m. EDT, eclipse 5:06-7:13 a.m., peaks at 6:08 a.m.
Resolute: sun up all day, eclipse 4:32-6:36 a.m. CDT, peaks at 5:33 a.m.
TYPES OF SOLAR ECLIPSES
Back in August of 2017, a spectacular total solar eclipse was visible from a narrow strip of the United States. Along this path, the Moon appeared to completely cover up the Sun's disk for several minutes. During this time, while the Sun was safely tucked away behind the Moon, it was even safe to remove your eclipse glasses! This allowed viewers to catch a glimpse of the beautiful solar corona before having to put the glasses back in place for when the first beads of sunlight poked out from behind the limb of the Moon.
This view of the August 2017 solar eclipse was captured from Scottsville, Kentucky. Credit: Justin Dickey, Unsplash
Elsewhere during the event, such as up here in Canada, only a partial eclipse was visible. The farther from the path of totality you were, less of the Sun was covered by the Moon, even at maximum eclipse.
Viewers had to wear their eclipse glasses or use a pinhole camera or other indirect way to watch the whole time. With only part of the Sun covered up, looking at it for any significant amount of time, even just a few moments, would risk damage to your eyes.
An annular solar eclipse looks so different from a total solar eclipse due to the Moon's distance and thus its apparent size. As the Moon travels around the Earth, it follows an elliptical orbit. So, sometimes it is closer to Earth, and other times it is farther from Earth. If an eclipse happens when the Moon is closer to Earth than usual, it appears large enough to completely cover the Sun's disk. If the Sun, Moon and Earth line up when the Moon is farther away, though, the Moon doesn't block all of the Sun's light. Instead, it leaves a ring of the Sun's disk around it.
The annular solar eclipse of 2012. Credit: Nakae/Wikimedia Commons
There is a brief safe moment to look at a total solar eclipse without eye protection, right when the Sun is completely covered by the Moon. In contrast, there is no safe time to do so during an annular eclipse.
6. Watch it when it’s a deep orange color (only) at sunrise
You should never view the Sun with the naked eye … with one very specific exception. If you are going to watch the sunrise—as with any sunrise, regardless of an eclipse taking place—it can briefly be safe to take brief glances with your naked eyes, but ONLY when it’s on the horizon and looking very orange. “While the Sun near the horizon may be bright, the spectral content of its radiation has relatively little short-wavelength light and thus the risk of retinal injury is much lower,” said Dr. Ralph Chou, Professor Emeritus at the University of Waterloo’s School of Optometry & Vision Science at Ontario, Canada, and an world-renowned expert on eclipse eye safety. “Once the Sun is more than a fist-width above the horizon … it greatly increases the risk for photochemical retinal injury.”
There is a caveat on a perfectly clear, haze-free day even a rising Sun can be too bright to look at. So you’re going to have to use your judgement on the day, not mine. Think about the clarity of the sky, and think about the color of the Sun. It’s must be orange. If it’s above the horizon and turning yellow, forget it. If you don’t trust your own judgement, then forget it. Err on the side of caution.
A partial solar eclipse as seen during sunrise in the coastal town of Gumaca, Quezon province, . [+] southeast of Manila on May 21, 2012. Thousands turned their eyes to the sky on both sides of the Pacific to gaze excitedly as a partial eclipse occluded the sun at dawn in Asia and at dusk in the western United States. An annular eclipse occurs when the moon passes in front of the sun, but is too far from the Earth to block it out completely, leaving a "ring of fire" visible. AFP PHOTO/TED ALJIBE (Photo credit should read TED ALJIBE/AFP/GettyImages)
Why You Shouldn't Even Glance At The Solar Eclipse Without Glasses
So, you want to watch the solar eclipse on Mon., Aug. 21. Good! You should! The U.S. is in the path of totality for the first time in most of our lifetimes, and it probably won't be again in our lifetimes — this isn't an event to miss. However, if you do choose to watch the solar eclipse, you might be wondering when you really need to wear solar eclipse glasses to watch the planetary event. I mean, surely if you look up at the eclipse during full totality, it'll be dark enough for your eyes to be protected?
Absolutely not. If there is one thing you absorb from reading this article, please, please make sure it is this: You must wear NASA-approved solar eclipse glasses (aka, not your regular sunglasses) the entire time you are looking up at the eclipse. No taking them off for just a second, no even glancing out your window without the glasses on to get a peek before you head outside. It's extremely dangerous for your eyesight, and could lead to temporary or even permanent blindness.
Why? The reason is pretty complex, but the gist is basically that when we look up at the sun in all its eclipseless glory, our eyes know to put up shields, so to speak, to protect the delicate inner workings of themselves — for instance, our pupils shrink rapidly so that less light enters the eye. We're still left with a bright spot in our field of vision after looking at anything bright, but because of these safeguards, it's just temporary. Damage occurring during an eclipse might not be, though. Because the sun is dimmed a substantial amount during an eclipse, our eyes can't adjust like they'd normally be able to while looking up at the sun. The pupils remain dilated, and what little sunlight that's visible behind the moon shines directly into our eyes. That can cause serious damage. So, the glasses act as a shield, allowing you to safely look up at the solar eclipse without hurting yourself.
The glasses, again, must be NASA-approved — you can't just wear any old sunglasses, even if they're designer. The standard for the lenses as released by NASA are ISO 12312-2. Additionally, if the glasses are at all scratched, do not wear them.
Now, none of this means you should be scared of the solar eclipse — again, it's going to be an amazing sight to see! Just ensure you take all of the proper precautions while viewing it, because it could seriously save you a lot of pain and trauma in the long run.
How To Watch The ‘Ring Of Fire’ Solar Eclipse On June 10
PHILADELPHIA (CBS) – This week the sun and moon will work in tandem to serve up a feast for the eyes. Set a reminder for Thursday, June 10, so you don’t miss the “Ring of Fire” solar eclipse. This partial or annular solar eclipse will be created as the moon passes in front of the sun.
On this date, however, the moon on its elliptical orbit of the Earth will be positioned too far from the gazes of Earthlings to completely cover over the sun. This will leave visible a bright annulus, or ring, around the moon’s silhouette at mid-eclipse. This effect inspired the name “ring of fire” eclipse.
Not everyone in the U.S. will be lucky enough to witness this exhilarating phenomenon, but we in the Delaware Valley will! The annular solar eclipse will be visible across the Northeast, Mid-Atlantic, and portions of the Southeast and Midwest, and Northern Alaska. In greater Philadelphia, the celestial event will be in progress at sunrise, but the maximum eclipse will occur after sunrise.
The eclipse will last for approximately 1 hour and 40 minutes in total. The eclipse path begins in Ontario, Canada then circles across the Earth’s northern latitudes. At the path’s midpoint, the greatest eclipse will occur over northern Greenland at noon local time. Afterward, the annular eclipse path passes over the North Pole and ends at sunset over northeastern Siberia.
Remember, it is never safe to look directly at the sun, even in the case of a partial eclipse. When observing, you must wear solar viewing or eclipse glasses throughout the entire eclipse. Regular sunglasses are not safe for viewing the sun. You can use an indirect method, such as a pinhole projector. Pinhole projectors shouldn’t be used to look directly at the Sun, but instead to project sunlight onto a surface.