He talks about that as the threshold between burn injury and non burn and I believe the key phrase was that vision "basically" returns to normal. I would like to know what he meant by basically and would like to have questioned him more on long term effects. I've seen the green flash a few times and that is enough for me, I'm done looking for it, I've always considered it pretty risky. The times the sun turns red is usually with flat horizon like over the sea or with lots of smoke or smog. When the sun sets over the mountains to the west of SL it is rarely red.
Chou is speaking to a select audience, I do wonder what he would say to a less discerning group. Erik Eric,
Dr. Chou clearly states the threshold of damage occurs at between 40 and 100 seconds. This is covered at 8:15 in the video. Have a closer look. It is both on the slide being presented as well as the narative. Yes, it was me who mentioned it on this board, but only as a statement of surprise regarding the facts presented in the video. I am not an expert in this area, but Dr. Chou is recognized as such. My mention of this statement is to be considered as a quote from Dr. Chou's presentation. He also states that these are NOT thermal burns. The rise in temperature is between 1.5 and 3 degrees C - hardly enough to create a thermal burn. (Presented on the same slide as mentioned above, at 8:15 in the video.) The damage is chemical in nature, although he refers to the phenomenon as a burn several times. I too know people who have caused permanent damage to their retina from looking at solar eclipses. It is real. I do not look at the sun for more than about a half second unless it is near the horizon and I am looking for the green flash. Please note that Dr. Chou states clearly that once the sun has reddened near the horizon that it is safe to look at. Specifically he states that if the sun is within one solar diameter of the horizon it can be safely observed without optical filters. It is still uncomfortably bright, and I only catch a glimpse until it is just about to disappear below the horizon. At that time I will watch for several seconds, maybe three of four, to catch the green flash. DISCLAIMER: This discussion is referring to observing the sun WITHOUT optical aid - i.e. magnification of one.
From: "erikhansen@thebluezone.net" <erikhansen@thebluezone.net> To: Utah Astronomy <utah-astronomy@mailman.xmission.com> Sent: Wednesday, May 23, 2012 1:22 PM Subject: Re: [Utah-astronomy] safe observing
He mentions one study and says it is mostly photochemical but thermal injury can occur and he seems to talking about glimpses without protection. He definitely does not advocate looking without protection and no eye doctor would as well. He seems to advocate protected sex as well.
The study should also follow-up these individuals in 20 years to really see what the radiation exposure has done. I recall it was you saying 40 sec exposure would not do permanent damage, I did not hear Dr. Chou say that.
Go to this site and watch the video. It is a presentation by Dr. Ralph
Chou. Dr. Chou is a noted expert on eye safety and viewing the sun. He has written at least two articles for Sky and Telescope that I am aware of. There are some really good facts on this site: http://www.transitofvenus.org/june2012/eye-safety
From: David Bennett <dlbennett@mac.com> To: Utah Astronomy <utah-astronomy@mailman.xmission.com> Sent: Wednesday, May 23, 2012 9:43 AM Subject: Re: [Utah-astronomy] safe observing
Wow, 40 seconds? Where did you read that one? Sounds very risky even during the maximum of an annular (don't call me annual) eclipse. I glimpsed for about 1/4 a second unprotected during the maximum from Salt Lake with the hopes of seeing an after-image with closed eyes...it barely worked but I wouldn't risk my sight doing any more.
On May 23, 2012, at 09:08 AM, erikhansen@thebluezone.net wrote:
With a few posts talking about exaggerated claims of the dangers of solar observing during an eclipse.
Did anyone try to glimpse the eclipse without eye protection? After all, it was said to can look for 40 seconds without permanent eye damage.
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