8 ms·

Eclipses and Decibels

82 points by ash 9y ago

Trombone12 9y ago
Excellent science writing! It is rare to see such quality here.
mjhoy 9y ago
Interesting. I was in Wyoming and noticed this as well. During the partial eclipse it was impossible to tell that the sun was dimming except that I could measure this with my camera's light meter. My friend hardly believed me when I informed her the sunlight had been halved three times (losing three stops) -- except that we could feel this difference in how chilly it had become. It is only as the last bit of sun is obscured that the world goes dark in any noticeable way.
- athenot 9y ago
  It was also fun to notice the street lights & home outdoor lights all come on in what looked like sunny day. The brain really compensated for the dimness.
- et-al 9y ago
  Oh crap, I sunny-16'd during the partial portion of the eclipse and dropped down to 4/30 @ 400 iso during totality. Wonder how my shots are going to turn out. :(
- ctdonath 9y ago
  Totality dropped the ambient temperature 8°F by me.
- russdill 9y ago
  I forgot to set the feature on time lapse mode that adjusts light levels. Oops. https://www.youtube.com/watch?v=JsJTYSehyZY https://www.youtube.com/watch?v=JsJTYSehyZY
teraflop 9y ago
A slight correction: according to some measurements that I found [1], the ambient illumination during totality is roughly 2-5 lux, which is "only" about 45dB below normal. (Full daylight is about 10^5 lux.) 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. [1]: http://www.strickling.net/sofi_eng.htm http://www.strickling.net/sofi_eng.htm
- russdill 9y ago
  I think for me the think that it really drove home is that the sun is really really really really bright.
learn_more 9y ago
You must remember that the irises in your eyes are dialating as the sun is being eclipsed. If that was not happening, you would undoubtedly notice the change in visible light like you do the heat.
- rcthompson 9y ago
  The dilation of your pupils is actually only responsible for a small portion of your eyes' ability to adjust to ambient brightness. The rest is your rods and cones adjusting their sensitivity biochemically.
nayuki 9y ago
> When the sun is completely blocked by the moon (which appeared about 3% larger than the sun during this particular eclipse), the total power delivered becomes 0% for a while, which is -infinity dB 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.
- dahart 9y ago
  Bummer that a nit that small would change your summary and overall emotional response, and prevent you from enjoying a great blot post, especially when the author pointed it out. "0%" is numerically accurate to at least 3 significant figures, isn't it? 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.
  - nayuki 9y ago
    The author's rushed approximation of "-infinity dB" is disingenuous, and discounts the efforts of people who handle low-level signals. 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.
madengr 9y ago
I have a plot of WWVB radio propagation here, for several days about the eclipse: https://zenodo.org/record/851609 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.
- th0ma5 9y ago
  Probably not ideal, but I know that PyEphem can be used to figure out relative positions of all of these at arbitrary times from a given location.
Stratoscope 9y ago
As anyone who has experienced totality knows, the difference between a total eclipse and the deepest partial eclipse is not just a quantitative change. 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.
- Florin_Andrei 9y ago
  > 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. 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.
  - Stratoscope 9y ago
    Finally, someone who knows the truth! 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-warning-after-being-partially-blinded-by-1963-eclipse 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...
idlewords 9y ago
It's not true that you don't perceive the darkening of the sun until just near totality. Instead, what you get is a really weird subliminal creepy feeling that something is wrong. 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.
- grzm 9y ago
  I concur with the "creepy" feeling. I wasn't in the path to experience the full eclipse and it was slightly overcast, and wasn't even aware of the exact time of peak occlusion where I was. However, I still noticed that something wasn't quite right. Noticeably peculiar.
- ctdonath 9y ago
  Yup, it's a "had to be there" thing. Complete eclipse, start to finish, took 3 hours. Totality was just over 2 minutes. Most of the time, lighting can only be described as "odd" - as you put it, color balance of full sunlight for brightness of sunset. Bugs & animals picked up on it, rapidly heading into night mode. Humans tended to stand around slowly realizing "huh? that's odd". Lighting starts as a sense of just wrong. Then at about 95% totality (!) you finally perceive the rate of change, as it exponentially plunges into darkness. Then you realize the darkness isn't, you're seeing with the visibility of a nightlight (but color balance still that of full sunlight), and proceed to freak over the visibility of the corona surrounding a big, well, black hole where the sun was. The horizon is also oddly bright. 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.
  - Florin_Andrei 9y ago
idlewords 9y ago
The main source of light during totality is the ring of daylight around the horizon. It looks like sunset in every direction. 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).
- russdill 9y ago
  It looks weirdly different as everything about it is backwards. Blue sky is beyond the sunset, but the light is coming from above you.
marcosscriven 9y ago
I went to view totality for the first time, in Salem, and thought exactly the same thing; I ended up putting a jumper on as I felt a little chilly, even though there was a mere sliver of the photosphere visible. It's curiously satisfying (I suppose because it's affirmative) to see one's subjective experience described objectively like this though.

82 points by ash 9y ago

Excellent science writing! It is rare to see such quality here.

Interesting. I was in Wyoming and noticed this as well. During the partial eclipse it was impossible to tell that the sun was dimming except that I could measure this with my camera's light meter. My friend hardly believed me when I informed her the sunlight had been halved three times (losing three stops) -- except that we could feel this difference in how chilly it had become. It is only as the last bit of sun is obscured that the world goes dark in any noticeable way.

athenot 9y ago
It was also fun to notice the street lights & home outdoor lights all come on in what looked like sunny day. The brain really compensated for the dimness.
et-al 9y ago
Oh crap, I sunny-16'd during the partial portion of the eclipse and dropped down to 4/30 @ 400 iso during totality. Wonder how my shots are going to turn out. :(
ctdonath 9y ago
Totality dropped the ambient temperature 8°F by me.
russdill 9y ago
I forgot to set the feature on time lapse mode that adjusts light levels. Oops. https://www.youtube.com/watch?v=JsJTYSehyZY https://www.youtube.com/watch?v=JsJTYSehyZY

teraflop 9y ago

A slight correction: according to some measurements that I found [1], the ambient illumination during totality is roughly 2-5 lux, which is "only" about 45dB below normal. (Full daylight is about 10^5 lux.) 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. [1]: http://www.strickling.net/sofi_eng.htm http://www.strickling.net/sofi_eng.htm

russdill 9y ago
I think for me the think that it really drove home is that the sun is really really really really bright.

learn_more 9y ago

You must remember that the irises in your eyes are dialating as the sun is being eclipsed. If that was not happening, you would undoubtedly notice the change in visible light like you do the heat.

rcthompson 9y ago
The dilation of your pupils is actually only responsible for a small portion of your eyes' ability to adjust to ambient brightness. The rest is your rods and cones adjusting their sensitivity biochemically.

nayuki 9y ago

> When the sun is completely blocked by the moon (which appeared about 3% larger than the sun during this particular eclipse), the total power delivered becomes 0% for a while, which is -infinity dB 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.

dahart 9y ago
Bummer that a nit that small would change your summary and overall emotional response, and prevent you from enjoying a great blot post, especially when the author pointed it out. "0%" is numerically accurate to at least 3 significant figures, isn't it? 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.
- nayuki 9y ago
  The author's rushed approximation of "-infinity dB" is disingenuous, and discounts the efforts of people who handle low-level signals. 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.

madengr 9y ago

I have a plot of WWVB radio propagation here, for several days about the eclipse: https://zenodo.org/record/851609 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.

th0ma5 9y ago
Probably not ideal, but I know that PyEphem can be used to figure out relative positions of all of these at arbitrary times from a given location.

Stratoscope 9y ago

As anyone who has experienced totality knows, the difference between a total eclipse and the deepest partial eclipse is not just a quantitative change. 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.

Florin_Andrei 9y ago
> 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. 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.
- Stratoscope 9y ago
  Finally, someone who knows the truth! 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-warning-after-being-partially-blinded-by-1963-eclipse 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...

idlewords 9y ago

It's not true that you don't perceive the darkening of the sun until just near totality. Instead, what you get is a really weird subliminal creepy feeling that something is wrong. 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.

grzm 9y ago
I concur with the "creepy" feeling. I wasn't in the path to experience the full eclipse and it was slightly overcast, and wasn't even aware of the exact time of peak occlusion where I was. However, I still noticed that something wasn't quite right. Noticeably peculiar.
ctdonath 9y ago
Yup, it's a "had to be there" thing. Complete eclipse, start to finish, took 3 hours. Totality was just over 2 minutes. Most of the time, lighting can only be described as "odd" - as you put it, color balance of full sunlight for brightness of sunset. Bugs & animals picked up on it, rapidly heading into night mode. Humans tended to stand around slowly realizing "huh? that's odd". Lighting starts as a sense of just wrong. Then at about 95% totality (!) you finally perceive the rate of change, as it exponentially plunges into darkness. Then you realize the darkness isn't, you're seeing with the visibility of a nightlight (but color balance still that of full sunlight), and proceed to freak over the visibility of the corona surrounding a big, well, black hole where the sun was. The horizon is also oddly bright. 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.
- Florin_Andrei 9y ago

idlewords 9y ago

The main source of light during totality is the ring of daylight around the horizon. It looks like sunset in every direction. 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).

russdill 9y ago
It looks weirdly different as everything about it is backwards. Blue sky is beyond the sunset, but the light is coming from above you.

marcosscriven 9y ago

I went to view totality for the first time, in Salem, and thought exactly the same thing; I ended up putting a jumper on as I felt a little chilly, even though there was a mere sliver of the photosphere visible. It's curiously satisfying (I suppose because it's affirmative) to see one's subjective experience described objectively like this though.