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Featured Stargazing U.S. Solar Eclipse of Aug. 21, 2017

  1. Aug 16, 2017 #241


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  2. Aug 16, 2017 #242

    jim hardy

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    I was in the autoparts store today and noticed welding goggle lenses.

    Took a #12 out to parking lot to look at sun and decided a single #12 isn't enough . It was mildly painful, as was a single #10 i tried last week. ...
    Got a #5 , it and the #12 together gave a quite comfortable image with no afterglow when i blink.

    So i bought two of each. about ten bucks total.

    Here's a picture through two #10's that i made last week, just held them over the lens on Fair Anne's Ipad:
    two #10's is so dark it took the Ipad quite a while to figure out there was an image present.
    I don't know if the numbers add like decibels, but two tens was a bit too dark and a single 12 was too bright.

    The guys behind the counter got enthused and tried to order a case of #12 lenses for themselves. Their suppliers are all sold out.

    old jim
  3. Aug 16, 2017 #243

    I like Serena

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    What will the weather be like?
    I remember going to Paris for the 1999 solar eclipse (on the edge of the millennium), only to find that the complete solar eclipse was obscured by a cloud!
    In the end I only experienced a partial solar eclipse.
  4. Aug 16, 2017 #244


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    I found something, then accidentally closed the window. It said that NASA recommends using #12 or higher welding goggles. The article said that many people feel like their eyes hurt with a #12, but #14 seems too dark, so I guess you have something, combining a #5 and #12. It must be some sort of logarithmic adding, like you suggested.
  5. Aug 16, 2017 #245
    A school I'm working with is taking a field trip to Greenville, SC to see it:


    They invited me, but I'm too busy to make a whole day of it. I'll probably step outside and have a peak from wherever I am in the SE on Monday, but frankly I don't get why people make such a big deal out of a shadow.

    I did happen to be in a great location for the eclipse of 1984 (New Orleans). Yep, it's darker. Kinda eerie. Not a big deal.
  6. Aug 16, 2017 #246
    Wasn't Paris in the totality zone in the Aug 11, 1999 Eclipse? I saw it from London. It was my 3rd and Cool! (1st in 1984 - annular, 2nd in 1994, 4th in 2005, - this is my 5th [a man is never happy! ...])
    What exactly do you mean by
    Because of the clouds? What difference does it make? Totality is totality ...

    In a sense, you're right. I agree. But seeing the sun's corona during totality is not just a shadow! It's a unique opportunity.
    Last edited: Aug 16, 2017
  7. Aug 17, 2017 #247


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    Yes, you can use your phone camera. But don't do long-term exposures (pointless anyway as the sun is so bright), and don't use additional lenses without a proper filter.
    Phone cameras don't have a shutter and can have the sun in view during normal use - they are typically built to survive a short (seconds) exposure, otherwise the cameras would break down frequently.
    According to this article, Apple confirms that iPhones can survive it, and NASA says that a few seconds with any type of phone should be fine. I didn't find the original statements, but it agrees with what I saw elsewhere as well.

    You don't see the corona and the diamond ring effect before/after it with clouds.
    You have the darkness, but apart from that it is just like a partial eclipse. Interesting, but not the reason why you go into the region of totality.
  8. Aug 17, 2017 #248
    I agree on one part:
    And you need no clouds to see it properly!

    But a clouded total eclipse is totally dark, while a partial one is not!* That's the difference and that's what I meant.

    * Unless on extreemly heavy cloudiness
  9. Aug 17, 2017 #249

    jim hardy

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    If you tried the #14 shortly after the #12 i think your eye might still be recovering , like at night when you're driving into bright Xenon headlights.
    What i noticed with two #10's is it's so dark that light from alongside and behind floods in and reflections make the image really hard to see.

    So i bought an inexpensive welding helmet with a #10 in it and taped the second one over the first. It works fine, blocks side light and will keep me from sunburning my face . I have an assortment of lenses so can find a comfortable combination that day. I will err toward conservative - might have to drive home after dark.

    . upload_2017-8-17_7-50-47.png
    Got one for Fair Anne, too.

    Home Depot, farm supply stores, and autoparts stores are likely places to find them not yet sold out.
  10. Aug 17, 2017 #250
    Just my luck...

    I bought a 10-pack of solar eclipse glasses on Amazon... Apparently Amazon is recalling them, as fakes, or knock-offs. The price should have been my first clue, I suppose...

    So, now I am looking for a solution in the 11th hour. Of course, all the welding supply houses are out of the lenses required.

    I do have some filter paper and binoculars, as well as an old K-Mart telescope with a solar filter, but sharing them between at least 4 people will be less than ideal, so I was hoping for a solution that scales to the individual.

    The guy at the welding supply store claims I can stack lenses, as long as they "add up to 12 or higher".

    I didn't find anything about that at the NASA website, so I thought I'd ask here.

    Can anyone speak knowledgeably on this subject, please?

    Do the shade numbers simply add together to get the right number? Can I really stack a shade #8 and a shade # 5 to get the same as a shade #13 lens?


    EDIT: NM, according to http://perkins.owu.edu/solar_viewing_safety.htm , you can not simply stack and add for a total. Thanks
    Last edited: Aug 17, 2017
  11. Aug 17, 2017 #251


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    Edit: As @mfb pointed out, total solar eclipses are common. What is special about this one? i heard on the radio that 90 million people live within 200 miles of the totality.
    Last edited: Aug 17, 2017
  12. Aug 17, 2017 #252


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    I wouldn't take that as a guarantee. I got the same email regarding glass filters for my telescope, which I bought from a reputable telescope supply company and tested (and am not going to use visually anyway). It's a paperwork problem. Do some homework on what you got -- they might be ok.

    Hmm -- reading the rest of the email and checking more, I see Amazon credited my account, de-listed the products and recommended I throw them away. That's insane. It hurts quality vendors and also as a stockholder is bad for business.
    Last edited: Aug 17, 2017
  13. Aug 17, 2017 #253
    The glasses I received lack the proper stamps/stickers designations for ISO standards. They do warn not to gaze at the sun more than three minutes, but when I looked at my ceiling lamp through them, the elements were clearly visible, and the bulbs were dimly visible. I don't think I got what I ordered....
  14. Aug 17, 2017 #254


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    It is over a somewhat densely populated region where most people speak English and internet access is widespread. It is natural that the topic is discussed a lot on English websites.

    The July 2009 eclipse went over the densely populated regions of India, Bangladesh and China, and a huge number of people saw it. But most of them are not on English websites, or don't have internet access at all.
  15. Aug 17, 2017 #255

    George Jones

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    My wife, daughter, and I are traveling, as the crow flies, about 1000 kilometres (620 miles) to see the eclipse.

    We will leave from north central British Columbia, Canada on Saturday morning, drive about ten hours to Seattle, and then stay Saturday night at our friends' house. On Sunday, we drive to a campsite (already booked by our friends) about 100 km (62 miles) from the centre of the eclipse zone

    The highway that we hopefully will take just reopened after being closed quite some time because of the forest fires. If it closes again (a definite possibility; current Weather Network headline "Wildfires will likely be enhanced by strong winds in BC interior"), the trip to Seattle will be more like eleven or twelve hours.
    Last edited: Aug 17, 2017
  16. Aug 17, 2017 #256

    jim hardy

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    It's difficult finding what the "SHADE" numbers mean.

    I found this on a photography referenced at a photography site.
    It references an ANSI standard which ought to be credible

    but i was unable to find the standard itself.

    Anyhow to your question , check my arithmetic and logic here ?
    If a #5 has nominal transmittance of 1.93 %
    two of them would transmit 0.01932 = 0.000372 = 0.0372% just about a number nine . That's almost an add but not quite....

    Taking square root of a #14 's nominal transmittance, 0.00027% = 0.0000027 , gives transmittance of 0.00164 = 0.164% which falls between nominal #7 and #8 (actually right on a #7's minimum).
    That's another 'almost add' .
    So i think they don't quite exactly add, but close enough for estimating.

    For two #10's i calculate 0.0139%2 = 0.0001392 =1.93 X10-8 = 1.93X10-6% and that's what i plan to use. I know it's plenty dark because i tried it.
    I also tried a #5 and #12 together for which i calculate 1.93% X 0.0019% = 0.0193 X 1.9X10-5 = 3.67X10-7 = 3.67X10-5% . I found that quite comfortable yesterday afternoon .
    I found a single #12 , 1.9 X10-3% painful.
    So i'm thinking i want transmittance less than 10-4%. That keeps me a decade away from pain.
    A single #14 is 2.7 X 10-4 % , myself i'd want darker. EDIT this line has been edited see below

    Note in the table how widely the maximum and minimum values bracket nominal .
    Since in multiplication we add exponents i think you can add welding shade numbers for purposes of estimating. They seem almost logarithmic per that table.

    Lastly , It's stressful converting units.
    Attenuation is inverse of transmittance , so i'd want attenuation greater than 1/10-4% , > 1/10-6 , > 106
    Maybe you'll find a diverse source to cross check me ?

    Believe me at my age i value what's left of my eyes.

    old jim

    LATE EDIT notice i fixed a mistake in this line it reads different from earlier.
    original was darker by a decade.
    Last edited: Aug 17, 2017
  17. Aug 17, 2017 #257
    Unfortunately, that math is way over my paygrade, so I will take your word for it.

    I get the gist, however.

    It leaves me with a question: "When stacking, does the effect translate to all wave lengths?"

    For example, are x-rays also cut the same as visible wavelengths, and therefore the stacking becomes safe in the x-ray spectrum, as well? The Website I quoted above suggests that they do not, but it may be more a question of whether stacking keeps them in the ranges of tolerance that are acceptable.

    Thanks for your input.
  18. Aug 17, 2017 #258
    My wife is leaving me to go to the southwest corner of Iowa for the eclipse. I have to stay home and watch the dog :cry:
  19. Aug 17, 2017 #259
    I guess the important question is, "Is she coming back afterwards?" :oldlaugh:
  20. Aug 17, 2017 #260


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    Wow, I'm totally shocked/stand corrected. This one mentions the GoPro too:

    Basically it says the lens is too small to bring in enough light to do damage.
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