The Wavy Track in an M1 Subframe
22 October 2026 · John
One 60-second frame of M1 (light_0046, 13 October 2026, 05:10 CDT, Huntsville) holds a thin, in-focus wavy track next to an ordinary straight streak. Its measured properties rule out aircraft, balloons, satellites, meteor trains and anything near the scope, and I could not identify it.
Background
I'm shooting M1, the Crab Nebula, again this year. Last year's image is here.
Each finished image is made from a large number of 60-second subframes that are stacked. Not every subframe is usable. Tracking errors, focus drift, airplanes and clouds all spoil frames, so before stacking I look at every one and delete the bad ones.
Satellites and meteors are rarely a problem. Their streaks are usually faint enough to disappear into the background noise once the frames are stacked.
This time I came across a frame and thought, "huh, that's weird." So, like anyone working out how to use the new AI tools, I asked Claude to look at it. The measurements and reasoning in the rest of this article are Claude's analysis of my original FITS files, and it is written up here as it happened: starting from a guess, being corrected by the data, and ending without a definite answer.
The frame
Light_0046 is a 60-second exposure of M1 through an O3S2 dual-band filter, taken with a Celestron EdgeHD 8 (203 mm aperture, about 2,000 mm focal length) and an ASI2600MC Pro on an AM5 mount. The FITS header gives DATE-OBS 2026-10-13 10:10:06 UTC, which is 05:10 CDT, so the filename carries local time. The site is Huntsville, Alabama (34.70° N, 86.58° W per the header).
At that time M1 stood roughly 77° above the horizon, near the meridian, and the Sun was about 22° below it. Both figures are my own approximate calculations, not header values. The plate scale is 0.39 arcsec per pixel and the field is about 0.67° × 0.45°.
The wavy track runs along the bottom of the frame as you see it in a PNG preview (row 0 at the top). The straight streak is at lower right. Left to right is roughly north on the sky.
The two tracks
Both tracks run north–south on the sky, within about 2° of each other. The straight streak is a plain, uniform line. The wavy track is the odd one.
- Panel A: the track enters at the left frame edge as a gentle wave of nearly constant wavelength, with amplitude growing steadily.
- Panel B: further along, the waves become tall arcs about 2′ high with sharp downward cusps, then fade out inside the frame.
- Panel C: the straight streak starts abruptly mid-frame, runs parallel to the wavy track about 2′ to one side of where it fades, and leaves the frame.
What the data show
The track is a real, point-like, steadily glowing source with a smooth growing wiggle, and it is in focus, so it is far away.
| Property | Value | How it was measured |
|---|---|---|
| Exposure | 60 s, 10:10:06–10:11:06 UTC | FITS header |
| Direction | North–south along Dec, both tracks within ~2° | Plate solution (WCS) in the header |
| Wavy track length | About 31′ (0.51°), left edge to where it fades | WCS positions of the traced path |
| Minimum angular speed | At least 31″/s | Track length ÷ 60 s |
| Wavelength | About 114″ (147 half-res px), steady | Spacing of 10 clean wave peaks |
| Wave amplitude | 9″ peak-to-trough, growing to 56″ over the first 22′, then arcs about 2′ tall | Traced path, detrended |
| Cycles | Roughly 14 | 10 clean waves plus the large arcs |
| Width | 2.2″ FWHM (5.8 px) against 1.9″ (4.9 px) for the stars | Profile fits across the track and across 245 stars |
| Implied distance | Roughly 35 km or more | Defocus: blur ≈ 203 mm × 2,003 mm ÷ distance |
| Brightness along track | Steady to about ±15% over most of its length, dimmer at the far end | Mean excess per column, 6 bins |
| Colour (R : G : B share) | 0.32 : 0.34 : 0.34 for the wavy track, 0.32 : 0.37 : 0.30 for the straight streak | Bayer planes, background-subtracted |
| Neighbouring frames | No track in 0045 or 0047 | Ridge-filter search of the full frames |
The colour is flat across red, green and blue, and the straight streak matches it. That points to broadband light, not a single-colour LED, though the dual-band filter limits how much that can say.
What it cannot be
Every ordinary candidate fails on at least one measurement.
| Candidate | Verdict | Why |
|---|---|---|
| Insect, bat, bird, hair or spider silk near the scope | Ruled out | An object at distance d is smeared to about 203 mm × 2,003 mm ÷ d on the sensor: roughly 11 px at 10 km and over 1,000 px at 100 m. The track is only about 1 px wider than a star. |
| Aircraft or drone | Ruled out | An airliner at 12 km would be about 9 px wide, plus it could not wiggle sideways by an arcminute every few seconds. |
| High-altitude balloon with a swinging payload | Ruled out | Needs 0.2 g early on and 1–3 g in the big arcs at the nearest allowed distance. A payload on a few metres of line cannot swing 10–20 m. |
| Satellite | Ruled out for the wiggle | Orbits are smooth. A tumbling satellite flickers in brightness; it does not move sideways. |
| Meteor persistent train | Unlikely | Trains at about 90 km are typically tens of metres or more across, so tens of arcseconds wide and fuzzy. This track is as sharp as a star. A train would also lie along the meteor's path, not beside it. |
| Mount, tracking or vibration | Ruled out | Any camera motion would copy the same wiggle onto every star. The stars are round. |
| Sensor or electronics artifact | Not excluded, but unlikely | A smooth 2-D curve that grows steadily, stays at constant brightness and has a sky-like colour does not resemble read noise, banding or amplifier glow. |
Why no real object fits
A real object at 35 km or more would need to accelerate sideways at roughly 0.2 g to over 100 g, depending on distance and speed.
The estimate assumes the source crossed the visible 31′ in at most 60 s, so the wave period is at most about 3.7 s (114″ ÷ 31″/s). For a sideways oscillation of semi-amplitude A at angular frequency ω, the acceleration at distance d is ω² × A × d.
- Nearest allowed distance (35 km): about 0.2 g for the early waves, 1.2 g for the later waves, and 2.7 g for the big arcs.
- Farther away or faster: every case gets worse. At 100 km the big arcs need roughly 8 g; doubling the track speed quadruples all of these.
No balloon, aircraft, drone or satellite does that. Either the source is something that can move this way, or the motion is not the motion of a single physical object.
The neighbouring frames
Neither the frame before nor the frame after contains the track, or any other long streak.
- 0045 started at 10:08:49 UTC. It was dithered about 280 half-resolution pixels (3.6′) from 0046, so I aligned it using the stars before comparing.
- 0046 is the frame with the track, 10:10:06–10:11:06 UTC.
- 0047 started at 10:11:07 UTC, one second after 0046 ended, with no dither. If the source had kept going north at 31″/s it would have been inside the frame for its first 20 seconds or so. It is not there.
The track also fades out inside the frame. Whatever made it stopped being visible during this one exposure.
What is left, and how to test it
Two ideas survive, and neither is convincing. The first is an optical effect that moves a point of light without moving the stars, such as a reflection of a bright source outside the field. The second is a real, actively steered light source far away. Neither can be confirmed or excluded from one frame.
Checks you can run
- Satellite check. Use the field centre (RA 83.64°, Dec +22.17°) and the window 10:10:06–10:11:06 UTC on 13 Oct 2026. A GPS-class satellite near the zenith moves at roughly 40″/s, close to the speed this track needs. Historical element sets need a Space-Track account; Stellarium or a Skyfield script can then propagate them. This was not done because the analysis workspace could not reach satellite catalogues.
- ADS-B history. Search the window above within about 250 km of Huntsville. This is a cross-check only: the focus test already excludes aircraft, so a clean result confirms the conclusion and a hit would be surprising. Options are listed below.
- Meteor reports. Check the American Meteor Society and NASA all-sky camera reports for 13 Oct around 10:10 UTC. A bright meteor could explain the straight streak.
- Your own logs. Look at the ASIAIR guide log and the capture log for 10:10–10:11 UTC for any disturbance. The sensor temperature stayed at −15 °C across all three frames.
- Other imagers. Post the original FITS crop with the time and position (RA/Dec above) on AstroBin or Cloudy Nights. An imager within a few hundred kilometres shooting the same area would settle whether it was a real distant source.
Getting ADS-B history
ADS-B data could not be pulled from the analysis workspace, so this has to be done separately. These are the routes that could be confirmed or reasonably described:
| Source | What it gives | Notes |
|---|---|---|
| ADS-B Exchange data products | Global snapshots every 5 s since May 2020, plus per-aircraft traces | Free only for the 1st of each month; everything else is a commercial agreement. Check whether the live globe's replay mode covers 13 Oct. |
| adsb.lol history | Daily readsb trace dumps (gzip JSON), open-licensed | The 2024 archive is on GitHub. Check adsb.lol's site for a 2026 archive or its replay map. |
| OpenSky Network | Historical state vectors | Needs a registered account. |
| FlightAware, Flightradar24 | Historical tracks | Free history windows are short; a 9-day-old query may need a paid tier. |
In any of these, filter to 2026-10-13, 10:10–10:12 UTC, within about 250 km of 34.70° N, 86.58° W. Then look for tracks that pass within a few degrees of overhead (M1 was near 77° elevation).
Method and caveats
The raw FITS was read, each 2×2 Bayer cell was binned to one half-resolution pixel, a median-filtered background was subtracted, and the result was smoothed lightly for display. The track was traced with a ridge filter and a minimum-cost path; that trace is reliable out to about x = 1,850 half-resolution pixels, and the amplitude and wavelength figures come from that stretch. The height of the large arcs beyond it is read from the images. Sky positions come from the plate solution stored in the FITS header.
- Distance limit. It assumes the scope was focused at infinity and the source is point-like. The roughly 3 px of extra width gives about 35 km; treat it as 30–40 km, not a precise bound.
- Speed and acceleration. Both assume the source crossed the visible track within the 60 s. If it was visible for less time, the speed is higher and the acceleration far higher.
- Sun and elevation. The 22° and 77° figures are approximations.
- Not checked. Satellite catalogues and ADS-B data were not accessible.
- Earlier guesses retracted. Early in the conversation Claude suggested an insect, a bat or bird, and a swinging balloon payload. The focus test rules out the first two, and the acceleration estimate rules out the third.
Sources
- Frames light_0045, light_0046 and light_0047 (FITS headers and pixel data), supplied by the imager.
- ADS-B Exchange: sample and historical data products
- adsb.lol globe history 2024 (GitHub)
- AstroBin forum: "What kind of trail is this?" — a different case, a faint streak in an OIII frame that commenters identified as a spinning satellite.