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Tangentially, I've seen some weird stuff in the sky. I have a blog post on the back burner about how the habit of looking up into the sky has been rewarding to

Tangentially, I've seen some weird stuff in the sky. I have a blog post on the back burner about how the habit of looking up into the sky has been rewarding to me, and the cool stuff I've seen. Sometimes satellites have very strange motion relative to your position, similar to planets going retrograde. They can make "J" shapes that look very odd. The first time I noticed this, my friend and I followed it all the way to the penumbra and umbra of the Earth's shadow - it suddenly dimmed as it entered the penumbra, and then completely disappeared as it passed into the umbra. A sure sign of a satellite in orbit. If you want to spot satellites, the best way I've found is to pick three random stars and imagine them as a triangle. Watch to see if the triangle changes shape - that means one of them is moving. It's very easy to get confused if you're looking at just one star, eg, sometimes the clouds are moving but you mistake the clouds as stationary and see the star as moving. But if you pick 3, even if you have that illusion, you'll see that they don't move relative to each other. On two occasions - once in Berkeley, CA and once in Athens, Greece - I saw a red light moving through the sky, and I followed it as far as I could but I didn't see it enter the penumbra (which isn't to say it did or didn't, just that I lost sight of it). I just have no idea what that was, or if it was the same on both occasions. One time my friends and I saw a flashing white light in the sky. It would rapidly increase from 0 to full brightness, and then just as quickly disappear. It stayed in roughly the same place. My friend had a good hypothesis, which was that it was a helicopter with some kind of rotating light. I think my favorite is that once, I saw an airplane contrail collapse into a series of smoke rings. Contrails often form these clumps of cloud, sort of like rain drops. These ones must have been very circular, because each one became a giant ring. You can see the clumps I'm talking about here: https://images.all-free-download.com/images/graphiclarge/contrail_sky_clouds_227799.jpg https://images.all-free-download.com/images/graphiclarge/con... There's pictures of rings on image search, but it looks like they came from the plane's engine, not from the mechanism I describe.

maxbond 3y ago
I'd like to add that it's really easy to find satellites, so I encourage people to try it. I can usually spot one in about half an hour (though my viewing conditions are about as good as they can be in a city, YMMV). Shortly after sundown or before sunrise is the easiest time, but I've found them at other times of night too. If I find myself outside at night, I try to spend at least a couple minutes looking for them (or whatever else there is to see, shooting stars, interesting clouds, Zodiacal lights, ...). You'd be surprised how much you can see if you spend a couple minutes regularly over a long period of time, especially relative to the minimal effort involved. (That being the thesis of the blog post.)
mikeyouse 3y ago
Sounds like Crow Instability that can be seen with large airplanes (https://en.wikipedia.org/wiki/Crow_instability https://en.wikipedia.org/wiki/Crow_instability) https://epod.usra.edu/blog/2011/08/crow-instability-in-contrails.html%20 https://epod.usra.edu/blog/2011/08/crow-instability-in-contr... https://epod.usra.edu/blog/2015/05/hybrid-contrails-with-crow-instability.html https://epod.usra.edu/blog/2015/05/hybrid-contrails-with-cro...
- maxbond 3y ago
  [ES: Informed speculation] I think it's a different mechanism, I think it's more like when you squeeze a drop of food coloring into water. I think it's something along the lines of, the friction on the outside of the drop and the momentum of the fluid on the inside of the drop impose a force in opposite directions, causing the fluid to spin, resulting in a vortex; because the cross section is a near perfect circle, this rotation is balanced, and you get a toroidal vortex. I imagine that, the bigger your drop, the more error you can tolerate in your circle. So by the time you get to the scale of, say, a caldera[1], there's a lot of room for error. (That's a slightly different mechanism, but I think comparable in this way.) The photos don't look like what I saw. They weren't oriented like that (they were hanging down like the clumps, perpendicular to the planes direction of motion), and they weren't so well formed. They were more lumpy. But this was a couple years ago and I didn't take a picture, so I can only go off of my recollection, and my strictly intuitive understanding of the fluid dynamics from the thousands of rings I used to blow smoking Black & Mild in my mispent youth. (You can also see rare and interesting rings that way, but I wouldn't recommend it!) Very cool stuff that I'm pumped to know about and will look out for though. Thanks! [1] https://66.media.tumblr.com/e0dd679a1c62751f09e702d8c005b9a1/tumblr_p5vbu5GHSg1sq04bjo1_1280.jpg https://66.media.tumblr.com/e0dd679a1c62751f09e702d8c005b9a1...

maxbond 3y ago

I'd like to add that it's really easy to find satellites, so I encourage people to try it. I can usually spot one in about half an hour (though my viewing conditions are about as good as they can be in a city, YMMV). Shortly after sundown or before sunrise is the easiest time, but I've found them at other times of night too. If I find myself outside at night, I try to spend at least a couple minutes looking for them (or whatever else there is to see, shooting stars, interesting clouds, Zodiacal lights, ...). You'd be surprised how much you can see if you spend a couple minutes regularly over a long period of time, especially relative to the minimal effort involved. (That being the thesis of the blog post.)

mikeyouse 3y ago

Sounds like Crow Instability that can be seen with large airplanes (https://en.wikipedia.org/wiki/Crow_instability https://en.wikipedia.org/wiki/Crow_instability) https://epod.usra.edu/blog/2011/08/crow-instability-in-contrails.html%20 https://epod.usra.edu/blog/2011/08/crow-instability-in-contr... https://epod.usra.edu/blog/2015/05/hybrid-contrails-with-crow-instability.html https://epod.usra.edu/blog/2015/05/hybrid-contrails-with-cro...

maxbond 3y ago
[ES: Informed speculation] I think it's a different mechanism, I think it's more like when you squeeze a drop of food coloring into water. I think it's something along the lines of, the friction on the outside of the drop and the momentum of the fluid on the inside of the drop impose a force in opposite directions, causing the fluid to spin, resulting in a vortex; because the cross section is a near perfect circle, this rotation is balanced, and you get a toroidal vortex. I imagine that, the bigger your drop, the more error you can tolerate in your circle. So by the time you get to the scale of, say, a caldera[1], there's a lot of room for error. (That's a slightly different mechanism, but I think comparable in this way.) The photos don't look like what I saw. They weren't oriented like that (they were hanging down like the clumps, perpendicular to the planes direction of motion), and they weren't so well formed. They were more lumpy. But this was a couple years ago and I didn't take a picture, so I can only go off of my recollection, and my strictly intuitive understanding of the fluid dynamics from the thousands of rings I used to blow smoking Black & Mild in my mispent youth. (You can also see rare and interesting rings that way, but I wouldn't recommend it!) Very cool stuff that I'm pumped to know about and will look out for though. Thanks! [1] https://66.media.tumblr.com/e0dd679a1c62751f09e702d8c005b9a1/tumblr_p5vbu5GHSg1sq04bjo1_1280.jpg https://66.media.tumblr.com/e0dd679a1c62751f09e702d8c005b9a1...