Eclipses and Decibels
apenwarr.ca
apenwarr.ca
At the deepest partial phase, you see Baily's Beads and the Diamond Ring. This is still the sun's photosphere peeking through the moon's valleys, bright enough that it washes out the corona, and bright enough that you had better use eye protection. Only when the moon completely blocks the photosphere do you see the solar corona.
This is totality. This is where you no longer need (and can't use) the protective glasses or filters or pinhole projectors. During totality, you can view the corona with your own eyes, with no protection, and even with binoculars.
The difference between a 99.9% partial eclipse and a 100% total eclipse is not 0.1%. It is infinity.
The photosphere (diamond ring, etc) is not dangerous if you only see it for 1 or 2 seconds. It is prolonged, central-vision, fixed staring that takes more than a few seconds that is dangerous.
So when the diamond ring comes out, take one look at it. But that's it, one look. Then turn away and put your goggles on. You'll be fine as long as you don't linger beyond a couple seconds.
The problems begin when people keep staring at it fixedly beyond a handful of seconds.
> The difference between a 99.9% partial eclipse and a 100% total eclipse is not 0.1%. It is infinity.
Well put.
Indeed, at the end of totality in the 1979 eclipse, I kept looking at the diamond ring and Baily's beads for a second or two with my binoculars. It did not damage my vision at all.
In the weeks leading up to this year's eclipse, I almost felt like it was my civic duty to correct some of the misinformation that was going around in the media. I had a feeling that many thousands of people who went to considerable trouble and expense to go to the path of totality would miss it entirely, because they got scared into keeping their eclipse glasses on the whole time.
There was such a fear campaign going on, just like the one in 1979 when Oregon schools changed their hours to keep the children indoors during totality.
This TV report was a good example:
http://www.kptv.com/story/36143862/portland-man-shares-warni...
The gentleman in the report did unfortunately damage his vision by staring at the 1963 partial eclipse - for 20 seconds! Truly a sad thing, but in the video they kept talking about the dangers of staring at a partial eclipse, while showing photos of a total eclipse - as if there was no difference between the two!
I tried to set the record straight in the comments, but man, it was an uphill battle. Read the comments and weep...
You just get bright spots in your vision, so put on those eclipse glasses so you can actually see something.
You're seeing things with the brightness of a rainy day, and then with the brightness of sunset, but the color balance is that of full sunlight. For me at least it's very unsettling, and I wonder if other people experience it that way.
The uncanny feeling is quite visceral and a big part of the reason I think eclipses just have to be experienced. All kinds of alarms go off in your animal brain when the moon eats the sun.
This is not to take away from the author's very correct observation that the light effects only really kick in close to totality, I'd say with over 90% of the sun covered.
And yes, there's a huge difference between any perceivable percentage away from totality, and totality itself. We're talking fractions of a second making a difference between direct viewing vs rapidly going blind.
Thanks for sharing though! I wasn't able to experience the full eclipse so I love seeing others experience it.
To my eyes, close to totality (on either side) the light was a bit redshifted. Not much, but a little. The change seemed symmetrical before and after.
I've imaged the whole event. Looking at the disk of the Sun, the color is not the same everywhere. The edge definitely loses energy in the blue end of the spectrum - I believe for the same reason why blue light is dispersed more, compared to red, in Earth's atmosphere. So near totality, when you receive light only from the edge of the photosphere, it's normal that the spectral composition looks different.
It's just ... well ... a lot darker.
Shooting long-exposure slide film is a good way to confirm this (no colour adjustment possible).
Moonlight is has a slightly lower (that is, optically "warmer") colour temperature -- 4100K rather than 5000K.
Contrast with "daylight" vs. "tungsten" film colour balance: 5500K vs. 3200K.
https://physics.stackexchange.com/questions/244922/why-does-...
http://www.apogeephoto.com/white-balance-and-color-temperatu...
Or shooting long exposure with a digital camera that does not automatically adjust the color balance. E.g. take the raw data from the sensor, instead of a camera-generated JPEG.
(Much of my experimental night photography was conducted ... some time ago.)
Working with film was, um, exciting? Not sure if that's the right word. Anyway, mistakes were final. I remember deliberating on the settings for a really long time before pushing the button.
I took my (corrective) glasses off, and then felt confused when everything got blurry. Some part of my brain must have thought they were sunglasses.
I swear I could feel myself get more anxious when taking my glasses off didn't "fix the problem" - like the "animal brain" could remain calm as long as the dim light could be explained by something familiar.
As far as light goes I would compare it to a full moon. We are not used to having dim light come from above. We are only used to it coming from the horizon at sunrise or sunset. That's why the light felt "wrong"/
Also, it has the brightness of an overcast day, but the shadows are still sharp-edged, just dim.
It was kinda cool, but
> Instead, what you get is a really weird subliminal creepy feeling that something is wrong.
and
> The uncanny feeling is quite visceral and a big part of the reason I think eclipses just have to be experienced. All kinds of alarms go off in your animal brain when the moon eats the sun.
simply do not resonate with me.
We were driving across the totality zone as the partial increased from 30% to about 90%. There was almost no loss of "brightness" per se, but everything had this odd "haze" to it as you looked around without normal driving sunglasses. You knew something was different, but not in style of a sunset or cloud-obscured day.
Me: Walks outside (currently not cloudy).
Brain: "Tut tut, looks like rai-WAIT WHY ARE THERE HARD SHADOWS?"
I started researching this a few weeks ago after seeing a Reddit comment asking (paraphrased) "my house is just a couple miles outside the path of totality, is it really worth the trouble of finding a different spot to view the eclipse?" The answer is that even at 99.5% occlusion, the sky is still hundreds of times brighter than complete totality.
I wonder how dark an eclipse could get under optimal conditions (wide track, and heavy overcast all around except in the path of the shadow).
https://zenodo.org/record/851609
The ionosphere was doing strange things the entire day, and even past local sunset.
Does anyone know of a tool that plots the earth/moon/sun position on arbitrary days? I'd like to go back and figure out what was going on.
It's curiously satisfying (I suppose because it's affirmative) to see one's subjective experience described objectively like this though.
The total power delivered during a total solar eclipse is obviously not zero. The author even admits a few paragraphs down that the corona is visible - and it's what people enjoy viewing during an eclipse. This one numerically inaccurate phrase spoiled my enjoyment of the article, unfortunately.
For me, it's really interesting that there's a discrepancy between the heat you feel and the light you see, and I love the writeup that is explaining the primary reason why -- because our perception of brightness is logarithmic, but our sensation of heat seems more linear in this case.
The experience of being there and having it go cold before it got dark was startling, and I have to agree with the author, it's easy to see why this stuff caused so much emotional stir before science showed us how it all works.
There's a much larger source of error, btw, in using a straight decibel scale as a proxy for brightness. (Also admitted & linked in the article.) It just doesn't matter, it's close enough, it's true, it's interesting, and it supports the narrative.
For example, his claim makes it impossible to compare the ambient light level of an eclipse versus the light level from a full moon or new moon.
For example, not knowing the noise floor will make it impossible to tell whether a 16-bit audio recording, or 20-bit, or 24-bit is the best choice.
What is the "larger source of error" in using a decibel scale for brightness? Maybe the fact that human eyes are not perfectly logarithmic? But such a scale is very appropriate for calculating camera exposures.
You can't take something out of context and claim that it's insulting people that he wasn't talking about. He wasn't discounting anyone. Yours is a bigger and more intentional error than his statement that totality is 0% energy. You're picking a fight instead of acknowledging that totality really is approximately 0% solar power for the purpose of figuring out how much heat you're going to feel on your arm during the eclipse, compared to before the eclipse.
He admitted the noise floor is not really zero. He wasn't contradicting himself, he was clarifying for the sake of the nit pickers. You're using that against him instead of accepting that both of his statements can be true at the same time. He was never claiming absolute zero with infinite precision, that is completely clear from the article.
He also wasn't asking what bit depth to use for audio recording. That would be weird, wouldn't it? Because he's talking about the sun's heat and not the sound it makes. He wasn't talking about photographing it either, or even measuring the heat precisely. He was showing why it gets cold before it gets apparently dark. You can do that in even less than 16 bits.
Yes, human eyes are not perfectly logarithmic. Interesting that you don't care for the sake of camera exposures in the middle of a conversation about the sun and moon, where you just cited bit depths and people who handle low-level signals. The logarithmic approximation isn't particularly good, which the link in the article discusses in detail. Log is good enough for this article, but not for vision scientists. The logarithmic brightness approximation really truly breaks down when you look at the sun or the night sky, human vision does not give an approximately logarithmic response to either the sun or the night sky, not even close. Camera film and camera sensors also break down and begin to clamp at either end of a moderate log range that is narrower than human vision. Photographing the corona well is really hard due to the extreme dynamic range and the way that camera response stops being logarithmic at the ends.
Even during totality it's not as dark as night. It's around the illumination of just after sunset, and he could have definitely plotted that - it's not that hard to lookup how much there is then, he doesn't have to measure it himself.
Does the correct number for solar power during totality explain why it gets cold before it gets dark?
The article was not wrong, it was an approximation, which he stated clearly. Did you perhaps not understand this sentence: "Anyway, there is never really "zero" radiant energy to detect. In reality there's always some kind of background noise, maybe at -90 dB or so."?
If he had used the correct number, you would see that it is approximately 0% power. Again, and I'll state it as fact now rather than rhetorical question, the article was accurate to more than 3 significant figures.
BTW, the discrepancy between night time levels and the darkness of totality is due in part to atmospheric scattering during the eclipse, so you're introducing a red herring.
> he could have definitely plotted that
Given that the heat plot goes from 0% to 100%, and that the brightness plot goes from -70dB to 0dB, will you estimate for me how many pixels in both plots would be different if he used really precise numbers for solar power during totality? My current estimate is 0 pixels would change across both plots. Do you think the number is higher? If so, why?