Do unicorns next
December 3, 2024 9:28 AM Subscribe
You're Probably Wrong About Rainbows is a Veritasium deep dive into the physical processes by which rainbows form. YouTube, 27m10s
It's pretty thorough.
The only important point that I think Derek misses here is that when you're looking at a rainbow, you're not actually looking at an arch so much as along and through the edge of a cone, whose tip is at your eye and within which lie all the droplets that contribute to your own personal rainbow. Which is why, if you look really carefully at the pot-of-gold regions, you'll see the "ends" of the rainbow continuing faintly below the horizon.
Those ends are typically much fainter than the above-horizon portion of the rainbow because so much of that part of the cone gets cut off by the plane of the ground, so the below-horizon portions of the rainbow are coming mostly from droplets relatively close to the tip of the cone, and Cones are MESSED UP (Numberphile, YouTube, 18m52s)
It's pretty thorough.
The only important point that I think Derek misses here is that when you're looking at a rainbow, you're not actually looking at an arch so much as along and through the edge of a cone, whose tip is at your eye and within which lie all the droplets that contribute to your own personal rainbow. Which is why, if you look really carefully at the pot-of-gold regions, you'll see the "ends" of the rainbow continuing faintly below the horizon.
Those ends are typically much fainter than the above-horizon portion of the rainbow because so much of that part of the cone gets cut off by the plane of the ground, so the below-horizon portions of the rainbow are coming mostly from droplets relatively close to the tip of the cone, and Cones are MESSED UP (Numberphile, YouTube, 18m52s)
The mathematical physics of rainbows and glories by John A. Adam for more detail.
posted by oonh at 10:05 AM on December 3, 2024 [4 favorites]
posted by oonh at 10:05 AM on December 3, 2024 [4 favorites]
I was recently driving out of a storm in northern CA, across a very flat and open area. I rainbow developed and I could see the complete 180 degrees of it and see it hitting the ground on both sides. it was perfectly full and vivid and more vibrant than any other I have seen. it was difficult to keep my eyes on the road!
posted by supermedusa at 10:14 AM on December 3, 2024 [1 favorite]
posted by supermedusa at 10:14 AM on December 3, 2024 [1 favorite]
And while his summation of Grant's series on refraction is pretty good (for Veritasium), if you want to see the rest, it's here:
Part 1
Part 2
Part 3
Part 4
Which is just sort of mindblowing. Once you've gone through those, did we ever talk about how holograms work? It sort of builds on some of the same reflection/refraction phase physics, and when you're done you'll feel like you understand stuff in a way that you might not have, before.
posted by Kyol at 10:24 AM on December 3, 2024 [4 favorites]
Part 1
Part 2
Part 3
Part 4
Which is just sort of mindblowing. Once you've gone through those, did we ever talk about how holograms work? It sort of builds on some of the same reflection/refraction phase physics, and when you're done you'll feel like you understand stuff in a way that you might not have, before.
posted by Kyol at 10:24 AM on December 3, 2024 [4 favorites]
You always see the same rainbow, and everybody else sees a different one.
posted by grog at 10:30 AM on December 3, 2024
posted by grog at 10:30 AM on December 3, 2024
hey wanna feel old? double rainbow guy was 15 years ago. yeah, I know.
posted by Rhomboid at 11:31 AM on December 3, 2024 [1 favorite]
posted by Rhomboid at 11:31 AM on December 3, 2024 [1 favorite]
I feel like the thing that unnerved me most about this video was the scenes in which he hauls a glass sphere around a room with an active laser, but doesn't appear to have eye protection or reflection guarding set up in a way I'd expect. I'm sure I just missed something in all the angles, but for all the colours he was dealing with he should have had an array of protective shields everywhere.
posted by rum-soaked space hobo at 11:54 AM on December 3, 2024 [1 favorite]
posted by rum-soaked space hobo at 11:54 AM on December 3, 2024 [1 favorite]
This video is truly fantastic, and I say that as someone with an Astrophysics degree -- for nearly all videos of this kind, I usually get to the end and say "yeah I knew all that, and either it was/wasn't a great way to convey the info" but there are several things I learned that I didn't know before (that a rainbow is brighter within the arc and why), and things I didn't really fully appreciate the implications/result (i.e. the maximum-angle thing).
But also, where's his PPE, man? Don't play with green or blue lasers without lots of protection because even very brief glints can put you into the target audience of the kinda-joke-but-not-really sign which says "DANG!!! DO NOT LOOK INTO LASER WITH REMAINING EYE"
posted by tclark at 12:14 PM on December 3, 2024 [6 favorites]
But also, where's his PPE, man? Don't play with green or blue lasers without lots of protection because even very brief glints can put you into the target audience of the kinda-joke-but-not-really sign which says "DANG!!! DO NOT LOOK INTO LASER WITH REMAINING EYE"
posted by tclark at 12:14 PM on December 3, 2024 [6 favorites]
I got a bachelor's degree in physics 35 years ago. For my whole adult life I've been telling myself that I should figure out rainbows on my own rather than reading about them. But I haven't done that. So perhaps I will watch this video.
posted by neuron at 3:42 PM on December 3, 2024 [1 favorite]
posted by neuron at 3:42 PM on December 3, 2024 [1 favorite]
This was a genuinely excellent piece of science communication.
posted by fantabulous timewaster at 6:58 PM on December 3, 2024 [2 favorites]
posted by fantabulous timewaster at 6:58 PM on December 3, 2024 [2 favorites]
While we're here, I'd like to read a decent understandable article about how sunsets and sunrises refract different colours.
posted by ovvl at 8:00 PM on December 3, 2024 [1 favorite]
posted by ovvl at 8:00 PM on December 3, 2024 [1 favorite]
As in different from each other, or different from when the sun is more overhead? Because the second one is very easy: that's all about Rayleigh scattering, the very same effect that makes the sky blue.
Rayleigh scattering involves electromagnetic radiation being deflected by particles much smaller than its wavelength. For the range of wavelengths that make up visible light, the particles that cause Rayleigh scattering are about the size of air molecules. Any given molecule is much more likely to scatter a shorter-wavelength (bluer) photon than a longer-wavelength (redder) one, so the more air there is between a source of white light and a detector, the redder will be the light that makes it all the way along the straight path from source to detector.
Consider the case when the sun is high in the sky. There's about one atmosphere-thickness worth of air between you and the sun, and passing directly through that doesn't redden up the light very much.
But the closer the sun gets to the horizon, the more oblique becomes the angle of any direct ray from sun to you with respect to the ground. That puts a longer air path in between, and the direct light correspondingly gets reddened up more.
You know that late afternoon light, where sunset is coming but isn't yet here, and the sunlight is just golden and the colours of everything it touches really pop? That's sunlight being reddened up a little bit by having a few extra atmosphere-thicknesses in the direct path between sun and surface.
When the sun gets really low in the sky there are many atmosphere-thicknesses worth of air in the direct path between you and it, so the direct light gets reddened up a lot.
To see how this works, draw yourself a diagram with a couple of concentric circles, with the outer one only just bigger than the inner one. The inner circle represents the surface of a planet and the outer one represents the limits of its atmosphere. Put a dot at the top of the inner circle to represent you standing on the surface.
Draw a ray starting at that dot and going straight up to represent light coming from directly overhead, and another ray starting at the dot and going horizontally to represent direct light arriving at sunrise or sunset. See how much longer the segment of ray between the inner and outer circles is for the horizontal ray compared to the vertical one?
posted by flabdablet at 9:20 PM on December 3, 2024 [4 favorites]
Rayleigh scattering involves electromagnetic radiation being deflected by particles much smaller than its wavelength. For the range of wavelengths that make up visible light, the particles that cause Rayleigh scattering are about the size of air molecules. Any given molecule is much more likely to scatter a shorter-wavelength (bluer) photon than a longer-wavelength (redder) one, so the more air there is between a source of white light and a detector, the redder will be the light that makes it all the way along the straight path from source to detector.
Consider the case when the sun is high in the sky. There's about one atmosphere-thickness worth of air between you and the sun, and passing directly through that doesn't redden up the light very much.
But the closer the sun gets to the horizon, the more oblique becomes the angle of any direct ray from sun to you with respect to the ground. That puts a longer air path in between, and the direct light correspondingly gets reddened up more.
You know that late afternoon light, where sunset is coming but isn't yet here, and the sunlight is just golden and the colours of everything it touches really pop? That's sunlight being reddened up a little bit by having a few extra atmosphere-thicknesses in the direct path between sun and surface.
When the sun gets really low in the sky there are many atmosphere-thicknesses worth of air in the direct path between you and it, so the direct light gets reddened up a lot.
To see how this works, draw yourself a diagram with a couple of concentric circles, with the outer one only just bigger than the inner one. The inner circle represents the surface of a planet and the outer one represents the limits of its atmosphere. Put a dot at the top of the inner circle to represent you standing on the surface.
Draw a ray starting at that dot and going straight up to represent light coming from directly overhead, and another ray starting at the dot and going horizontally to represent direct light arriving at sunrise or sunset. See how much longer the segment of ray between the inner and outer circles is for the horizontal ray compared to the vertical one?
posted by flabdablet at 9:20 PM on December 3, 2024 [4 favorites]
Differences between the way the light looks at sunrise compared to sunset will mostly be related to dawn air being cooler than dusk air, having had all night to cool down rather than all day to warm up.
Warm air is more energetic and will consequently tend to contain more stirred-up solid particulate matter than cool air. On the other hand, cool air is more likely to be loaded up with water mist droplets than warm air.
All of these things come in a range of sizes much larger than air molecules, and the specific mix of particles present will affect the colour and degree of diffusion of transmitted light via Tyndall scattering which has a similar colour-filtering effect to Rayleigh scattering, and Mie scattering which doesn't.
posted by flabdablet at 9:33 PM on December 3, 2024 [3 favorites]
Warm air is more energetic and will consequently tend to contain more stirred-up solid particulate matter than cool air. On the other hand, cool air is more likely to be loaded up with water mist droplets than warm air.
All of these things come in a range of sizes much larger than air molecules, and the specific mix of particles present will affect the colour and degree of diffusion of transmitted light via Tyndall scattering which has a similar colour-filtering effect to Rayleigh scattering, and Mie scattering which doesn't.
posted by flabdablet at 9:33 PM on December 3, 2024 [3 favorites]
Y’all have got to read Light and Color in the Outdoors.
The physics is intr or mid-undergrad level, but it has excellent descriptions of rainbow effects (yay Airy functions), sundogs, mirages, and various other weird things light does outdoors.
posted by nat at 12:33 AM on December 4, 2024 [3 favorites]
The physics is intr or mid-undergrad level, but it has excellent descriptions of rainbow effects (yay Airy functions), sundogs, mirages, and various other weird things light does outdoors.
posted by nat at 12:33 AM on December 4, 2024 [3 favorites]
This video is truly fantastic, and I say that as someone with an Astrophysics degree
I have an optical physics PhD, and there were parts of that I didn't even know. (Mostly the part about how each band of color is actually a caustic.)
posted by OnceUponATime at 11:14 AM on December 4, 2024 [3 favorites]
I have an optical physics PhD, and there were parts of that I didn't even know. (Mostly the part about how each band of color is actually a caustic.)
posted by OnceUponATime at 11:14 AM on December 4, 2024 [3 favorites]
A new episode from Veritasium always goes to the top of my YT queue.
He did a nice 3 part doco for TV a few years back on the story of uranium.
posted by Pouteria at 1:38 AM on December 5, 2024 [1 favorite]
He did a nice 3 part doco for TV a few years back on the story of uranium.
posted by Pouteria at 1:38 AM on December 5, 2024 [1 favorite]
> While we're here, I'd like to read a decent understandable article about how sunsets and sunrises refract different colours.
A flashback to "red sky at night, sailor's delight; red sky at morning, sailor take warning." I always assumed this folk weather prediction had something to do with blue-scattering aerosols and cloud formation. But including temperature as a variable is also interesting.
When I was in high school, we were riding the bus to school on a day with a predicted snowstorm, and as we admired the brilliant sunrise, one of my friends said, "Sailor take warning, baby! The snow today will be great!" The temperature fell from 70⁰F to 20⁰F over the next few hours and we (eventually) got several feet of snow, and school dismissed early. I ended up walking home through the falling snow using a shortcut through the woods, with the girl I was dating; I don't remember if there was some problem with the buses or if I just knew it was a chance to make some amazing magic memories.
posted by fantabulous timewaster at 7:45 AM on December 5, 2024 [1 favorite]
A flashback to "red sky at night, sailor's delight; red sky at morning, sailor take warning." I always assumed this folk weather prediction had something to do with blue-scattering aerosols and cloud formation. But including temperature as a variable is also interesting.
When I was in high school, we were riding the bus to school on a day with a predicted snowstorm, and as we admired the brilliant sunrise, one of my friends said, "Sailor take warning, baby! The snow today will be great!" The temperature fell from 70⁰F to 20⁰F over the next few hours and we (eventually) got several feet of snow, and school dismissed early. I ended up walking home through the falling snow using a shortcut through the woods, with the girl I was dating; I don't remember if there was some problem with the buses or if I just knew it was a chance to make some amazing magic memories.
posted by fantabulous timewaster at 7:45 AM on December 5, 2024 [1 favorite]
Thank you for the reflections on sunsets and sunrises. I am particularly interested in how surrounding clouds sometimes turn bright pink at tentative moments before or after sunsets. Which probably has to do with complex interactions of slanted sunlight on the horizon beaming through moist (or polluted) air.
posted by ovvl at 3:33 PM on December 6, 2024
posted by ovvl at 3:33 PM on December 6, 2024
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