I just watched a SmarterEveryDay video about a shot of the blood moon over a Saturn 5 rocket model (which is kinda interesting).

In that shot he got an unusual horizontal line across the moon intersecting the tip of the rocket.

enter image description here

I think this is a bit interesting and my guess is that it is somehow to do with what a DSLR CMOS is doing, but I'm no photographer. I thought perhaps someone on here would have some idea about what it is and how it was caused.

Below are some more details he posted. What I think is particularly interesting is that it happened on multiple cameras, and also in the video feed.

It happened on all 3 cameras, but only from one of our 2 shooting locations. We were approximately 2.2 miles away. Here are the exact TPE data from this shot: http://app.photoephemeris.com/?ll=34.700583,-86.619095&center=34.7058,-86.6382&z=14&spn=0.05,0.14&dt=20180131063500-0600&sll=34.711166,-86.655948 I was shooting with a 300mm lens on a Canon 70D, also a 100mm lens on a Panasonic GH5. Trevor also saw it on his Canon7D MkII.

  • \$\begingroup\$ I am not knowing, My bet is that it has something to do with the light on the top of the rocket. \$\endgroup\$
    – Alaska Man
    Feb 5, 2018 at 9:52
  • \$\begingroup\$ It could be a bit of careless Photoshop? If the rocket was pasted as a separate layer, but the layer had not been thoroughly masked, then the upper edge of the layer might still show. \$\endgroup\$
    – MiguelH
    Feb 5, 2018 at 10:23
  • \$\begingroup\$ @Alaskaman that was my first guess, but the light is not shining in several of the photos (I believe it's blinking for aircraft) \$\endgroup\$
    – scottbb
    Feb 5, 2018 at 13:59
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    \$\begingroup\$ That's less than 30 miles from my home! \$\endgroup\$
    – Michael C
    Feb 5, 2018 at 18:29
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    \$\begingroup\$ The vast majority of DSLRs made in the past decade or more have CMOS sensors, not CCDs. I'm not aware of any current DSLR model that has a CCD sensor inside. \$\endgroup\$
    – Michael C
    Feb 5, 2018 at 18:31

3 Answers 3


My best guess is that it's a trail from a passenger jet flying through the scene, as it looks a bit uneven and inconsistent. That would also make sense given that only cameras from that site picked it up.

Investigating the contrail hypothesis - some planes were close to the sight line and in a theoretical range (no wonder... planes are everywhere).

wwww.flightradar24.com replay showing the approximate direction and distances: Flightradar replay

Visibility range calculated for a typical airliner altitude between 25000 feet (orange) and 35000 feet (blue) - generated on the heywhatsthat.com website visibility range

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    \$\begingroup\$ If you watch the video, the line moves with movement of the camera position to always be lined up with the tip of the rocket. A contrail would not do that. It was also recorded by three different camera/lens combinations. The likelihood of all three being perfectly aligned so that the tip of the rocket is perfectly lined up with an existing atmospheric phenomenon are astronomical. \$\endgroup\$
    – Michael C
    Feb 5, 2018 at 19:14
  • \$\begingroup\$ the rocket was not moving, it's the camera shake. as for the alignment, both cameras, despite slightly different locations, easily captured the same astronomical object - the moon - lined up with the rocket. from their location, both the moon and the hypothetical contrail are close to infinity. so the contrail appears to be quite plausible explanation, not referring to anything extraordinary. too bad it cannot be confirmed. \$\endgroup\$
    – szulat
    Feb 6, 2018 at 0:41
  • \$\begingroup\$ Then why is the "contrail" not visible on either side of the moon? Or below the moon before it slid behind the tip of the mockup? The sun was emerging from the horizon behind the cameras at the same time and would have illuminated any such cloud/contrail/etc. Instead of looking at one poor resolution frame grab, watch the video. That's nothing that was in the sky. It is some kind of optical effect caused by interaction between the light from the moon and the tip of the mockup. \$\endgroup\$
    – Michael C
    Feb 6, 2018 at 7:03
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    \$\begingroup\$ The photographer states that there were no planes in the area at that time. \$\endgroup\$ Feb 6, 2018 at 8:49
  • \$\begingroup\$ if it is contrail, look how thin the line is - must be extremely distant. it is dark. i doubt it could be normally seen even in a broad daylight, i would just disappear in the haze. but the moon acts as a slider viewer, revealing even smallest nontransparent objects blocking the light. \$\endgroup\$
    – szulat
    Feb 6, 2018 at 12:58

My two cents - Its a contrail (condense-trail) from an aircraft. Also turbulence in the wake of an aircraft can do this even if the temperature is too high for a contrail to form.

  • \$\begingroup\$ If you watch the video, the line moves with movement of the camera position to always be lined up with the tip of the rocket. A contrail would not do that. \$\endgroup\$
    – Michael C
    Feb 5, 2018 at 19:07
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    \$\begingroup\$ The photographer states that there were no planes in the area at that time. \$\endgroup\$ Feb 6, 2018 at 8:50

The tip of the "rocket" (it is actually a scale mockup of a Saturn V that was built in 1999) has an aircraft warning beacon. The beacon has a glass lens protecting it. Typically such protective lenses are cylindrical in shape with a hollow cavity in the middle where the actual beacon light is located. The light from the moon passing through and being refracted by the glass lens appears to be acting as a point source of light. The sun, which was just rising behind the cameras, may also be reflecting off the warning beacon's protective cover.

As some of the comments to the linked video theorize, the light passing through the cylindrical glass lens over the beacon is creating an interference pattern similar to what causes diffraction spikes. The effect is along only one axis due to the cylindrical shape of the glass lens covering the beacon.

From a comment by Ron Jones:

The tip of the rocket acts as a point source and becomes a source for light that has the same coherence of the direct moon light. The interference band is indeed a line of light and dark dots, but they are much dimmer than the moon light and look dark, sort of like the blazingly bright sun spots look dark against a much brighter sun. The tip of the rocket probably has a nice shiny tip, like the glass dome over a light. At a few miles distance, it becomes essentially a point source.

From a comment by Patrick Bryant:

I think what is happening is the interference of two paths to the eye (or camera), one along the line of sight and another which glances off of a reflective cylinder at the tip of the rocket. The glancing path picks up a 180 degree phase flip but the path length is well within a single wavelength of the normal line of sight path. The result is near total destructive interference for photons coming from the region of the moon perpendicular to the symmetry axis of the cylindrical mirror. Coherence is not needed because even single photons would experience this effect - the two paths interfere with themselves.

From a comment by Paper Burn:

a polarized red airplane warning light on top of the rocket the lens is a disk in a shape causing an optical diffraction Fraunhofer diffraction equation is used to model the diffraction of waves when the diffraction pattern is viewed at a long distance from the diffracting object, and also when it is viewed at the focal plane of an imaging lens.

And Patrick Bryant's reply:

If the cylindrical mirror (shiny metal rod) is vertical, then these two paths exist for the horizontal band perpendicular to the surface of the mirror. The dark band should extend the height of the reflective rod so if you put a taller rod, you could use this effect to make the entire moon dark from that vantage point.

In other comments the original poster of the video (Smarter Every Day) says that the same phenomenon was observed by three different camera/lens combinations: A 300mm lens on a Canon 70D, a 100mm lens on a Panasonic GH5, and a Canon 7D Mark II with unspecified lens that appears, from the video, to be an EF 200-400mm f/4 L IS 1.4X.

The line appears to be slightly tilted with respect to a line perfectly perpendicular to the vertical axis of the rocket mockup. I would not be surprised at all that a close inspection of the glass lens covering the warning beacon would reveal that the glass lens is slightly tilted at the exact same angle.

Regardless of the exact physical phenomenon that explains the line, it seems that the (cylindrical?) glass lens that covers the warning beacon and the moonlight that it refracted/reflected and/or the sunlight that it reflected is the key to what happened.

Any explanation that suggests an atmospheric phenomenon, such as a jet exhaust contrail, ignores the linked video, where the line moves with slight camera movements to remain exactly aligned with the tip of the Saturn V mickup. It also ignores the evidence from three different camera/lens combinations shooting from slightly different positions that all show the phenomenon perfectly aligned with the tip of the rocket.

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    \$\begingroup\$ the answer sounds like if someone replaced the word "magic" with "diffraction", assuming it would automatically make the answer scientific. no real claim was made, so it cannot be refuted (as usual with magic occurrences) but a simple reason why this kind of physics cannot be responsible for the dark line is that such patterns appear "on top" of objects causing it. telescope aperture causes star spikes or airy disc so they can appear anywhere in the aperture. diffraction/interference happening inside the rocket top would only be observed in the rocket top itself, not the horizontal line. \$\endgroup\$
    – szulat
    Feb 6, 2018 at 0:24
  • \$\begingroup\$ Diffraction is the answer that I think makes the most sense. The only issue is that as far as i can tell from reading this should have resulted in a light rather than dark line. \$\endgroup\$
    – undefined
    Feb 6, 2018 at 5:51
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    \$\begingroup\$ @MichaelClark no, polarizers aren't magical either. the wave becomes horizontal after the first filter. the next filter changes the angle to 45° (and the amplitude is reduced accordingly, removing the nonmatching component). 45°-rotated wave hits the second vertical filter and again, there is 45° mismatch so the amplitude is reduced further. in the end, we get vertical polarization. obviously, without the 45° stage the vertical filter blocks everything because there is no vertical component in the horizontally polarized light. no problem at all for the 19th century physics. \$\endgroup\$
    – szulat
    Feb 6, 2018 at 13:27
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    \$\begingroup\$ @MichaelClark i know this video and you are drawing incorrect conclusions. quantum theory introduced new rules of thinking about particles and also introduced new problems, like what what individual photons do. obviously, such questions cannot be answered by newtonian physics, where such objects do not exist. before Einstein light is simply the waves of aether and the theory agrees with experiments, including the case of 3 polarizers (as explained in my previous comment). if you don't mess with things traveling close to the speed of light the old newtonian physics is perfectly good even today. \$\endgroup\$
    – szulat
    Feb 6, 2018 at 19:41
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    \$\begingroup\$ yes, that's interesting. the old physics definitely fails when the observer or the observed objects are moving close to "c", but merely using the light for looking at things is okay. i guess that for most cases we can simply pretend that the light does not have any speed at all. it simply appears everywhere immediately. good enough approximation for almost everything we can see most of the time. \$\endgroup\$
    – szulat
    Feb 7, 2018 at 1:34

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