I need help identifying a blob.

Last night I took a picture of Polaris, and there is a weird blob in it that I can't identify. Star charts and other pictures on the 'net do not show this blob. I took three pictures (with slightly different positions) and the blob has the same shape and position (relative to Polaris) in each. The blob does not exist in other pictures that I took (pointing in completely different directions).

Taken with a Canon t5i, 300mm lens, 3 minute exposure on a motorized equatorial mount. Viewing conditions were terrible, with lots-o-moon and smoke from forest fires. From Colorado.

Polaris is the brightest star, slightly left and down from center. Yildun, the next star in the handle of the little dipper, is near the upper left corner. The blob in question is very near, and slightly up and to the left of Polaris.


Simple Lens Flare: I don't think it's lens flare (LF). With LF, you can draw a straight line through the photo where the flare, the bright object, and the center of the photo all line up. Also, the LF tends to match the shape of the bright object. I don't think it's LF because the blob doesn't line up with the center of the photo and a bright object, and there are no bright objects that have the same shape as the blob (with that weird tail to it). Also, I have three photos with the same blob. In each case, Polaris (the brightest point in the photo) moves slightly because the camera moved slightly but the blob moves exactly with Polaris and not somehow relative with the center of the frame.

Under careful analysis, there IS lens flare, but it is where you'd expect it and not where the blob is. If you draw a line though Polaris and the center of the frame, there is a flare on the opposite side of the center and the same distance away from the center as Polaris is.

Schmutz in the camera: I don't think it's dust/dirt in the camera/sensor. If that were the case then I would have seen it in other photos from the night, and I didn't. Also, the blob would have stayed in the same position in the frame and not moved with Polaris as it did in the 3 different photos that I have of it.

Not-So-Simple Lens Flare: Maybe. Although I cant imagine how this would happen unless some lens elements were not radially-symmetric and/or elements were not lined up on a common axis. But I don't know everything about camera design so maybe this is possible?

There's a new blob in the sky: Possible. Although I think the odds of "user error" are much higher. Maybe someone else wants to take a new photo of Polaris? (wishful thinking)

enter image description here

Polaris with weird blob[1]

  • $\begingroup$ Try uploading this to astrometry.net so you can at least see the RA/DEC of the blob. If this physical media, I'd guess it's a stain or defect in the film itself of in the developing process. If it's digital, not sure. $\endgroup$
    – user21
    Commented Sep 4, 2017 at 2:35
  • $\begingroup$ Looking around in the center I found this which is reminiscent of the original pair. The upper trail is roughly twice as long as all of the other objects, so if it's real, it's moving! Do either of the blobs in this correspond to real objects either? $\endgroup$
    – uhoh
    Commented Jan 29, 2018 at 8:41
  • $\begingroup$ This very much looks like lens flares or some internal reflections in your optics (is there a filter involved? Or maybe in front, if you image through some window or similar?). $\endgroup$ Commented Feb 27, 2020 at 13:04

2 Answers 2


That looks like a lens effect. Polaris is the brightest object and there is an internal reflection in the lens or the camera.

It's a nice photo under difficult conditions. Can you see NGC 188, an odd open cluster?

  • $\begingroup$ That really looks like internal reflection in the lens. Would have been interesting if you had another image with Polaris half way to the left edge of the frame. $\endgroup$ Commented Sep 4, 2017 at 2:52
  • 1
    $\begingroup$ I updated the question to include my thoughts on lens flair-- but I don't think that's it. I cannot see NGC 188. I played with the photo (playing with the levels, etc) and couldn't tease it out of the data. Jim G: I DO have other photos of Polaris from that night, where the camera moved slightly between shots. The blob moves relative to the stars, and not in some relation to the center of the frame. $\endgroup$ Commented Sep 4, 2017 at 15:56
  • $\begingroup$ @DavidKessner sorry, in the updated question you say "...the blob would have stayed in the same position in the frame and not moved with Polaris.." but in the comment above you say "The blob moves relative to the stars..." These appear contradictory, did you mean to say in your comment that the blob does not move relative to the stars? $\endgroup$
    – uhoh
    Commented Jan 29, 2018 at 10:20

Looking around in the central area, I found a 2nd pair of objects that do not look like stars. The upper one is a line but much longer than the trails of the other stars, and the lower one is also a fuzzy blob.

If neither of these correspond to real objects either, then you have some kind of contamination on your sensor perhaps. Your comment says ...The blob moves relative to the stars... in other exposures. If so, perhaps it does not move with respect to pixel coordinates?

As an aside, the short linear feature could possibly be a satellite in a very high orbit and so will appear to move quite slowly relative to the star field that your mount is tracking.

mystery blob crop 1 mystery blob crop 2

mystery blob crop


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