Why is this shooting star wavy or squiggly toward the end of it's visible streak

Question

I was taking photos of some stars when I noticed this shooting star was wavy toward the end (start?) of it's trail. My cousin suggesting that it could be the CCD in my camera or as it spiralling as it enters the atmosphere. This is a heavily cropped image

Shooting star

full picture

Wobbling or spiralling seems much more likely than CCD issues in this image. — Rory Alsop, Dec 27 '19 at 21:13
Of course it had already entered the atmosphere @Michael Beamish else how could we it? — Alchimista, Dec 28 '19 at 08:04
The stars have traces, suggesting your camera was not tracking. True? Does your camera have an internal "image stabilization" algorithm running? For that matter, we might need to dig into the readout order & FET switching to determine if there are pixel-drain artifacts ("bleeding" into neighbors) — Carl Witthoft, Dec 30 '19 at 22:44
@MichaelBeamish What type of camera where you using? Please be specific (i.e. not "mirrorless" but instead "Pentax K1 Mark II.") — Michael C, Jan 04 '20 at 13:50
The stars have jitters as well, they're just not as obvious. — Michael C, Jan 04 '20 at 13:51
@Michael C I'm using the Sony Mirrorless A7Rii with a SEL1635GM lens — Michael Beamish, Jan 04 '20 at 13:52
@Carl Witthoft I don't have tracking and I disable image stabilisation. Can you elaborate what FET switching is? — Michael Beamish, Jan 04 '20 at 13:54
@MichaelBeamish That camera has a fully mechanical shutter as well as the option to use electronic first curtain. Which option does the EXIF info indicate was selected for this photograph? — Michael C, Jan 04 '20 at 13:59
@Michael C I checked and I can't see in the exif data whether it was one or the other. I do know however that I have not got that setting enabled in the camera. — Michael Beamish, Jan 04 '20 at 14:21

score 3 · Answer 1 · answered Dec 28 '19 at 02:00

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It's shutter vibration. It begins at one end of the trail (which I'm guessing is the start of the exposure) and quickly damps out.

answered Dec 28 '19 at 02:00

uhoh

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I thought it might have been a spiralling object coming toward me. It is also likely that the electronic shutter was open and still as it was exposed for 25 seconds. It's not a typical DSLR shutter – Michael Beamish Dec 28 '19 at 07:21
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@MichaelBeamish how did you trigger the shutter? Did you have to touch the camera or use a remote control (e.g. IR or Bluetoosh)? – uhoh Dec 28 '19 at 09:03
It was on a 2 second delay, which is more than enough time to stabilise. The shaking would have to occur while the 'shooting star' was in motion to have affected it which is only a short amount of time isn't it? Like a split second? Also the stars are not blurry as it would have impacted them also right? – Michael Beamish Dec 28 '19 at 09:23
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@MichaelBeamish The vibration is a very small part of the exposure time (around 1%, if you measure the relative length on the trail) so the blur on the stars would be very hard to notice. – xenoid Dec 28 '19 at 10:22
The shooting star occurred while the shutter was open, which was for about 25 seconds. The shutter closed well after the event. The more I think about it, the less I believe it was vibration from the shutter. It could have occurred from something else, but long exposures mean that nothing is moving for a long time. What else could it be? – Michael Beamish Dec 28 '19 at 11:05
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@MichaelBeamish I see what you mean. Are you 100% sure is a meteor and not a satellite? Since they can move fairly slowly sometimes (1.4 down to 0.2 degrees/sec) if you just glance at intervals a satellite will look just like a non-distinct random star, we only know they are satellites when we watch for a while and notice them slowly creep against the other stars. I still think it's shutter vibration, but the trail is caused by an artificial satellite. – uhoh Dec 28 '19 at 13:40
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@MichaelBeamish There are many sites that will predict satellite trails for you. You can type in the approximate time and the date and your lat/lon cooridnates and websites will tell you the satellites that were passing then, even make a map for you. – uhoh Dec 28 '19 at 13:42
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@MichaelBeamish (there could have been a shooting star also, but this could still be a satellite in your image) There are many sites that will predict satellite trails for you. You can type in the approximate time and the date and your lat/lon cooridnates and websites will tell you the satellites that were passing then, even make a map for you. I'm still betting this is a satellite and that's shutter vibration. – uhoh Dec 28 '19 at 13:55
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From the shot duration and the length of the star trails, I have the math right the first arc would be a 120m wobble for an object in low orbit (100km). That would require some serious acceleration. Also in the shot was taken in the middle of the night, it can't be a satellite (there are in earth shadow). So if the wobble is an object move, it is much closer (plane). – xenoid Dec 28 '19 at 18:24
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More math: at 100km, given the length of the trail, the object moves at 1.4km/s, so it is not in orbit (8km/s minimum), to be in orbit it should be 6 times farther, but then the initial wobble is about a kilometer. – xenoid Dec 28 '19 at 18:32
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@xenoid I don't see any math yet, but if you have some that applies here then it would be really great if you posted it as an answer! The altitude determines how late or early a satellite can be seen. What you are saying is roughly correct for the ISS or other low objects circa 400 km, but an object can be much higher also and therefore be seen much later or earlier. Also assuming 400 to 1000 km altitude the associated velocity would be closer to 7.4 to 7.8 km/s LEO orbital velocity (1000 to 400 km). – uhoh Dec 29 '19 at 02:14
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@xenoid Without the elevation above horizon, we can't convert angular speed to orbital speed. Basically there needs to be more data (lat/lon, time, direction) before we can conclude anything with 100% about the visibility of a satellite in the photo. – uhoh Dec 29 '19 at 02:18
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@uhoh I'll get that shortly. Great discussion here, cheers. – Michael Beamish Dec 29 '19 at 03:03
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@uhoh the elevation of Warragul our town in Australia is 143m. I was facing approximately 58-60 degrees NE. The time was 920.19pm, on the 26th December. Warragul is 38.1538 S, 145.9298 E. I was on a manfrotto tripod was about 5-6' off the ground and angled approximately 50-60 degrees. Is this enough info? – Michael Beamish Dec 29 '19 at 03:24
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@MichaelBeamish That's great, thank you! Do you mean 21:20:19 local time, (which is UTC +11)? I think that's all that is necessary. From the star pattern I think we can reconstruct the exact direction using Astronomy.net (How (the heck) does Astrometry.net work?) – uhoh Dec 29 '19 at 03:32
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@uhoh yes 21:20:19 local. Sorry I didn't think to convert it – Michael Beamish Dec 29 '19 at 04:22
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Rather than shutter vibration, it might be an artifact of built-in image stabilization algorithms. I agree it appears to "damp out" but I don't see any intensity variation in the star images (which, moving much more slowly relative to the camera, if damping out would be brighter at the tail-end of the exposure). – Carl Witthoft Dec 30 '19 at 22:43
@CarlWitthoft below is a photo (basketball hoop) on the same night only a few minutes apart. The streak of the object is mostly clean. In this case you can see one end is much dimmer than the remainder. Is that what you mean?
https://imgur.com/fStkccE https://imgur.com/gsqAUBG
– Michael Beamish Jan 02 '20 at 22:36
@uhoh I had a closer look today and if you look at the image hosted at Imgur https://imgur.com/fStkccE you can see that the line is not straight along it's entirety whereby if you look at the shooting star in the other link https://imgur.com/gsqAUBG you can see it quite straight. Taken 2 minutes apart with approximately the same settings. I'm certain that the object has some sort of oscillation along its entire path that must accelerate or become more pronounced if it is coming toward us, but if it is headed away from us then the oscillation continues as it streaks away. What do you think? – Michael Beamish Jan 10 '20 at 12:09
@MichaelBeamish Oh I lost track of this, okay I'll have a closer look this weekend. Thanks! – uhoh Jan 10 '20 at 13:39

Why is this shooting star wavy or squiggly toward the end of it's visible streak

1 Answers1