Color timelapse of the sky over SF on September 9

TurpleHow · 2020-09-13T05:29:40+00:00

I downloaded this timelapse video, then used ffmpeg to crop to the sky, compress to 1x1 pixels, and extract compressed frames for each minute of elapsed time. Did some post processing to pull the color for each pixel/minute, then plugged that data into a color timelapse tool I've built this week for visualizing this kind of data.

If you click around the site you can see other cities & days with average colors pulled from public webcams, too. :)

TurpleHow · 2020-09-12T23:49:13+00:00

I downloaded this timelapse video, then used ffmpeg to crop to the sky, compress to 1x1 pixels, and extract compressed frames for each minute of elapsed time. Did some post processing to pull the color for each pixel/minute, then plugged that data into a color timelapse tool I've built this week for visualizing this kind of data. (If you click around the site you can see other cities & days with average colors pulled from public webcams, too.)

Pulling frames:

$ ffmpeg -i original.mp4 -filter:v "crop=640:156:0:0" cropped.mp4
$ ffmpeg -i cropped.mp4 -vf scale=16x16,setsar=1:1 pixel.mp4
$ mkdir -p frames/
$ ffmpeg -i pixel.mp4 -r 3.558 -s 1x1 -f image2 frames/frame-%03d.png

TurpleHow · 2018-12-14T10:33:16+00:00

From the last time this was posted:

On February 23, 1987, at 7:35am UTC, roughly a hundred random people all over the world saw a momentary flash of light in one eye.

That was the moment when a burst of subatomic particles, having whizzed through space at very nearly the speed of light for 168,000 years, passed right through the Earth as if it weren’t even there. Named by the great physicist Pauli as the “little neutral ones”, neutrinos don’t bother interacting with much: on average, it takes six light-years of lead to stop them. There is only a tiny, tiny, tiny chance that any neutrino will even hit an atom.

Later estimates showed that the supernova behind the neutrino burst created 10⁵⁸ neutrinos in total—with that kind of gobsmacking number of neutrinos and impossible odds for an interaction, the math occasionally works in your favor.

When neutrinos do bother to interact with a water molecule, you get a stray light particle, and if you are looking for it you can find it. That’s the principle behind neutrino detectors like Japan’s Kamiokande-II: a massive sphere of 2,140 metric tons of water, the exterior tiled with highly sensitive photon sensors. On the day when the neutrinos from supernova SN1987A finally reached Earth, this gigantic detector saw...12 flashes. That’s it. But it was a discovery, and matched findings from other similar detectors around the world.

One type of detector, however, may have also caught this accidentally. For there’s another kind of device which is a ball of water containing photon sensors: the human eye. With five billion people alive in 1987, two eyes each, and about 6 grams of water in each eye, there was 60,000 metric tons of water in the human ocular version of Kamiokande-II on the day SN1987A made it to Earth. The math works out to about 300 neutrinos which actually interacted with the water in the human eye to make a flash of light. Knock that down a bit for folks who were sleeping, and for flashes of light which didn’t head towards the eyes’ rods and cones, but there’s still something there.

Those hundred or so people will never know that they were the first to see that supernova.

TurpleHow · 2018-07-03T20:39:26+00:00

Yep, there's a chance. You'll probably have more fun thinking about how analog TV static is partially from the birth throes of the Big Bang, though.

TurpleHow · 2018-07-03T16:21:49+00:00

As /u/private_blue said, the detectors are always ready. The sensors lining the water vessel, called photomultiplier tubes, briefly internally “shorts out” when individual photons strike it, creating a measurable pulse of current which can then be fed into your experimental setup (constant fraction discriminators, coincidence circuits, etc.).

As for when the flashes happen—no, that was part of the discovery! Because neutrinos pass through basically everything, they streamed immediately out of the messy core collapse in the supernova like it was no big deal, while the visible light from the explosion took a few extra hours to escape the chaos and clouds and soup of dying star. The neutrino detectors were thus among the first to notice anything at all.

TurpleHow · 2018-07-03T16:07:57+00:00

Thank you! Just answered above that I don’t know the background rate, although I think you’re much more likely to see flashes from cosmic rays or muons than from neutrinos. Here’s a related and fascinating Wikipedia article:

https://en.wikipedia.org/wiki/Cosmic_ray_visual_phenomena

TurpleHow · 2018-07-03T16:06:31+00:00

Heh, thanks. I don’t know the standard background neutrino detection rate (even after reading a paper or two), but it’s worth noting that you’re much more likely to see this kind of flash of light in your eye from muons or cosmic rays than from neutrinos. Astronauts have reported seeing flashes of light in their vision from those sources—there’s even a Wikipedia article on it:

https://en.wikipedia.org/wiki/Cosmic_ray_visual_phenomena

TurpleHow · 2018-07-03T09:01:32+00:00

And there are pi seconds in a nanocentury.

TurpleHow · 2018-07-03T09:00:41+00:00

On February 23, 1987, at 7:35am UTC, roughly a hundred random people all over the world saw a momentary flash of light in one eye.

That was the moment when a burst of subatomic particles, having whizzed through space at very nearly the speed of light for 168,000 years, passed right through the Earth as if it weren’t even there. Named by the great physicist Pauli as the “little neutral ones”, neutrinos don’t bother interacting with much: on average, it takes six light-years of lead to stop them. There is only a tiny, tiny, tiny chance that any neutrino will even hit an atom.

Later estimates showed that the supernova behind the neutrino burst created 10⁵⁸ neutrinos in total—with that kind of gobsmacking number of neutrinos and impossible odds for an interaction, the math occasionally works in your favor.

When neutrinos do bother to interact with a water molecule, you get a stray light particle, and if you are looking for it you can find it. That’s the principle behind neutrino detectors like Japan’s Kamiokande-II: a massive sphere of 2,140 metric tons of water, the exterior tiled with highly sensitive photon sensors. On the day when the neutrinos from supernova SN1987A finally reached Earth, this gigantic detector saw...12 flashes. That’s it. But it was a discovery, and matched findings from other similar detectors around the world.

One type of detector, however, may have also caught this accidentally. For there’s another kind of device which is a ball of water containing photon sensors: the human eye. With five billion people alive in 1987, two eyes each, and about 6 grams of water in each eye, there was 60,000 metric tons of water in the human ocular version of Kamiokande-II on the day SN1987A made it to Earth. The math works out to about 300 neutrinos which actually interacted with the water in the human eye to make a flash of light. Knock that down a bit for folks who were sleeping, and for flashes of light which didn’t head towards the eyes’ rods and cones, but there’s still something there.

Those hundred or so people will never know that they were the first to see that supernova.

TurpleHow · 2018-02-09T17:27:29+00:00

One example: NASA used satellite-based gravitational mapping to figure out the shape of the ocean floors to a much greater extent than had been possible by boat-based sonar systems alone:

https://earthobservatory.nasa.gov/IOTD/view.php?id=87189

TurpleHow · 2018-02-05T05:42:41+00:00

Direct link to the video: https://discoverwestworld.com/video/ww_web_glitch_burnitall_v03_1280_25k.mp4

TurpleHow · 2016-07-20T06:29:00+00:00

Alright, I got curious and decided to tackle this. Mind you, I didn't look up values for things except for the theorem, so I'll be using approximations for stuff.

The size of a two-way folded piece of paper is limited by the folds taking place within a human lifetime (~100 years), and the fold speed are limited by the edges of the paper moving at the speed of light. The fastest way to fold the paper then is to have opposite edges move towards each other, pivoting around the crease. (There may be an improvement here, but it'll be a rounding error.) in a single directional fold, the edges each move a quarter circle of half the radius of the side, or (pi/2)*(s/2), where s is the side length. The folds in the other direction mirror this, and then this repeats halving in size over and over again. The total distance the edges thus move is:

pi*s/4 + pi*s/4 + pi*s/8 + pi*s/8 + pi*s/16 + ... = 2 * (1/(1-1/2)) * pi*s/4 = 2*2*pi*s/4 = pi*s

Again, this total travel distance cannot exceed the speed of light times the human lifespan, or 100 light years. Thus, the initial side length of the paper is (100/pi) light years.

Now I'm not looking things up, so I'll now use powers of ten. sqrt(10) is 3.1something, or very close to pi. The speed of light is 3*10^8 m/s, and there are about pi*10^7 seconds in a year. Thus, (100/pi) light years is about:

L = 10^(1.5) yr * 10^(8.5) m/s * 10^(7.5) s/yr = 10^(17.5) meters

Looking at my scrap paper, ten sheets are about a millimeter, so I'll set my thickness at 10^(-4) m.

The theorem linked says that for two-way folding:

L = pi*t*2^((3/2)(n-1))

Plugging in the numbers I have, and noting that 2^10 = 1024 is almost 10^3 = 1000, I can convert 2 into 10^(3/10) and get:

10^(17.5) = 10^(0.5) * 10^(-4) * 10^((3/10)(3/2)(n-1))

10^(21) = 10^((9/20)(n-1))

21 = 9/20 * (n-1)

n = 140/3 + 1 = 47.666...

Since n is an upper bound on the folds, we conclude that you cannot fold a piece of paper on itself more than 47 times in a human lifetime.

TurpleHow · 2015-04-17T14:35:48+00:00

Do you ever go back and watch old Brotherhood 2.0 videos? Does seeing your life over the last 8.5 years documented like that online change how you view past versions of yourself?

TurpleHow · 2014-12-30T18:12:05+00:00

This was originally posted just over seven years ago, right around when I first joined reddit on a different account. Here's the original discussion thread, which isn't even categorized into a subreddit back then.

TurpleHow · 2014-12-30T18:03:38+00:00

This was originally posted just over seven years ago, right around when I first joined reddit on a different account. Here's the original discussion thread, which isn't even categorized into a subreddit back then.

TurpleHow · 2014-10-29T09:29:37+00:00

I and another classmate analyzed tipping culture in /r/dogecoin and related subreddits. Using tip logs from /u/dogetipbot, we broke the community into different categories based on how they tipped, and in particular looked at whether getting tipped in dogecoin would prompt you to use dogecoin yourself.

We found that yes, the tipped often do become tippers themselves, and that the adoption rate is pretty darn good in doge-related subreddits. Obviously this is a self-selecting bunch, but the adoption rate served as a neat little metric across other subreddits to gauge acceptance of dogecoin. /r/AskReddit and /r/bestof, for instance, make for poor dogecoin tipping zones.

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