One important element to remember though is that the Moon's shadow will obviously become narrower as it is cast from the Moon to Earth (in a shape of a cone with the wide end being at the Moon and the narrow end on Earth). If an eclipse occurs during this time, it will be a Total solar eclipse because the Moon has totally obscured the Sun's disk, producing the beautiful solar corona ejecting outward from the Sun. When the Moon's orbit is toward its minimum distance from Earth, the Moon will appear visually as a larger disk than the Sun. Therefore the Moon's apparent size in our sky will vary by 13%. In fact, the Moon's distance from Earth varies from a minimum of 221,000 to a maximum of 252,000 miles. To understand the difference between a Total and Annular eclipse of the Sun, it must be understood that the Moon has an elliptical orbit around Earth.
Therefore a solar eclipse is a relatively rare phenomena and a Total or Annular eclipse even more rare, with the Hybrid eclipse the rarest of all. The Moon's orbit is titled 5 degrees to Earth's orbit around the Sun. A solar eclipse can only happen during a New Moon. I also stacked a pair of #12's and there was no sunlight visible.A solar eclipse occurs when the Moon passes between the Sun and Earth, casting the Moon's shadow on Earth. I think this is likely the end of the spectrum.any darker would make it too difficult to see. This was very dark, but the sun was still quite visible. Then, i put #10, and #9 together inside a dark welding helmet. I then put a combination of #12 and #5 together inside goggles with almost no ambient light (large pupils) and found this to be very comfortable and still plenty bright enough to watch the eclipse. This blocked 100% of the direct sun, but allowed indirect light to enter my eyeballs (like you would normally get while NOT looking directly at the sun) thus shrinking my pupils and felt much more comfortable. 12 seemed ok if i held just welding glass in my hands an inch or so from my nose. I found this to be a little too bright in a welding helmet where there is not much ambient light. 12 was the darkest glass they had.Īfter staring at the sun for a while with various combinations, Here are my observations. I bought the last of the welding glass off the shelf at the local shop today. The formula above are given in T and that is how the calculations were conducted. However, OSHA has lower safety standards for welders as they would permit SN11 minimally when ANSI and AWS say SN14. I would not use any combination of lenses that did not exceed the single SN of 14. Yeah! This works out to an SN15 (not 16), so better than SN14.Īs far as safety goes, - better safe than sorry.
A combined SN11 + SN5 give you a combined transmittance of 0.00000099. But the higher the numbers, the better the results. If you run the math here, two lenses with an SN of 2 will give you the transmittance of an SN of 3. But algebraic law of logarithms allow you to add the log of two numbers. Transmittance is a log function (non-linear) and therefore simple addition does not work with SN of multiple Welding lenses. Would we expect addition of lenses to be linear? Such as 2+2=4? No. According to the website, the UV and IR requirements are less stringent than the visible range and the calculations are more complex. Damage can occur in the UV and IR regions that could effect tactical vision or night vision within the periphery of the human range.
This equation is for the visible light range only as discussed on the link above. Please note the number of decimal places is off by an order of magnitude. A Shade Number 14 by the same equation has a T of 0.0000027. So rearranging again /7 = OD OD = 4.2857 plugging this into the first equation and multiplying both sides by (-) -4.2857 = log T Take the antilog of both sides to obtain T The antilog of -4.2857 is 5.1795 x 10-5 Transmittance of light T to the eye is 0.000052 with an SN11 Welders lens. If your shade number (SN) is 11 then 11-1 = 7/3 OD. Please see this link: and assuming the formula are correct.(found in several locations) I have copied it here because I am new and it didn't get into the correct area. I posted a link with calculations and other links.
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