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Arran townsend

Where Did This Star Come From?

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Hi all, I have recently been out trying to take some images with my barn door tracker I have built, a few nights ago I thought I'll try and photo C34 Veil nebula, and while going through all of my frames I noticed somthing which I can not explain 1 of my images shows a bright star randomly appearing, I'll post the image below along with the image before and the image after, I imideantly ruled out a satellite and I thought it could be an optical reflection of some sorts,

Image details:

Exposure: 15 seconds

ISO: 3200

Sensor temperature 24°C 

300mm lens aperture around f/7

IMG_6891.CR2 IMG_6890.CR2 IMG_6892.CR2

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This is interesting, not sure if I can provide an answer to the question though.

Might be some sort of transient feature - very interesting, as I've started a thread yesterday with idea of trying to find such transient features and their relation to Fast Radio Bursts.

This one has "expected signature" - star like flash that is obviously not cosmic ray hit - appearing only on one sub in the set.

Here is the thread for anyone interested:

 

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The red star on the right is 52 Cyg and the rogue star looks suspiciously the same, even down to the slight reddish flare. Could it be an imaging defect? Though, none of the other stars seem to have copied. Zooming in on Stellarium there is a faint dot of nebula right where this extra star appears. I'm not sure how accurate that is, as it seems to be a photo overlaid on genuine star coordinates.

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2 hours ago, DaveHKent said:

The red star on the right is 52 Cyg and the rogue star looks suspiciously the same, even down to the slight reddish flare. Could it be an imaging defect? Though, none of the other stars seem to have copied. Zooming in on Stellarium there is a faint dot of nebula right where this extra star appears. I'm not sure how accurate that is, as it seems to be a photo overlaid on genuine star coordinates.

I thought the same about the  reflection, but the star underneath the bright star on the right is not reflected under the star on the left, very strange...

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The transient star is more yellow than its permanent neighbour.

We should call NASA.

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1 hour ago, Ruud said:

The transient star is more yellow than its permanent neighbour.

We should call NASA.

Yeah we should :), i was thinking it might be a variable star of some sort

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I think I've posted before about a number of "transient" naked eye stellar type objects I've seen over the years. Some I've put down to retinal "flashes", visual apparitions caused by the eye's vitreous humor dragging on the retina during sudden eye movements. They are related to floaters which I happen to be plagued with.

Other flashes have almost certainly been real events - that is not due to visual effects. They lasted maybe 5 seconds, then faded rapidly. No movement was visible. I've seen plenty of satellite flares and I'm something of a plane spotter and have been confident the flashes were not conventional satellites or aircraft.

Momentary bright, stationary phenomena all before the drone era, except the most recent one and I've put that down to possible drone activity as it was low over towards the seafront - popular with drones.

So what gives? Unlikely to be stellar in origin. Nothing could build and shed that kind of energy so rapidly that didn't make the news! Satellite laser ranging? Maybe? Very stellar in appearance though. Not a military grade red or green laser then.

A flare off a Molniya satellite at Apogee? Possible I suppose. And that's my final answer. Imperfect but the best I can do!

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I would think what happened is the barn door moved briefly during the exposure.

52Cyg being the brightest star registered but non of the others were bright enough to register twice.

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Could this be a meteor moving along the axis of the lens? Explains why it's only in one frame, but alignment and magnitude could be just coincidence.

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2 hours ago, wxsatuser said:

I would think what happened is the barn door moved briefly during the exposure.

52Cyg being the brightest star registered but non of the others were bright enough to register twice.

That would be possible explanation if there were significant mismatch between brightness of two stars.

I'm not sure, but it does seem that "ghost" image is actually brighter than 52Cyg - it features horizontal diffraction spike (very faint) as well - not present on 52Cyg. Even if this diffraction spike is caused by lens and star position in FOV rather than intensity - they do both look to be about the same in intensity (or near). This would mean that about equal time of exposure is needed for both - other less bright stars would also have identifiable double in this case.

Meteor down the line of sight is plausible but very low probability event - if star image was at least a bit out of shape - elongated in one direction - that would be much much more likely scenario.

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6 hours ago, Roy Challen said:

Could this be a meteor moving along the axis of the lens? Explains why it's only in one frame, but alignment and magnitude could be just coincidence.

Very interesting point, I didn't think of that

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Posted (edited)
4 hours ago, vlaiv said:

That would be possible explanation if there were significant mismatch between brightness of two stars.

I'm not sure, but it does seem that "ghost" image is actually brighter than 52Cyg - it features horizontal diffraction spike (very faint) as well - not present on 52Cyg. Even if this diffraction spike is caused by lens and star position in FOV rather than intensity - they do both look to be about the same in intensity (or near). This would mean that about equal time of exposure is needed for both - other less bright stars would also have identifiable double in this case.

Meteor down the line of sight is plausible but very low probability event - if star image was at least a bit out of shape - elongated in one direction - that would be much much more likely scenario.

A meteor could explain it, if this strange appearance was a meteor coming perfectly toward the lens, I'll feel pretty proud that I've captured perhaps a 1 in a few million event, but meteors usually would break up into small parts at it's peak burn in the atmosphere and this is not shown in the image, or the image after, unless it burned up and dissipated in the 5 second gap between exposures.

Plenty of food for thought!

Edited by Arran townsend

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13 hours ago, Paul M said:

I think I've posted before about a number of "transient" naked eye stellar type objects I've seen over the years. Some I've put down to retinal "flashes", visual apparitions caused by the eye's vitreous humor dragging on the retina during sudden eye movements. They are related to floaters which I happen to be plagued with.

Other flashes have almost certainly been real events - that is not due to visual effects. They lasted maybe 5 seconds, then faded rapidly. No movement was visible. I've seen plenty of satellite flares and I'm something of a plane spotter and have been confident the flashes were not conventional satellites or aircraft.

Momentary bright, stationary phenomena all before the drone era, except the most recent one and I've put that down to possible drone activity as it was low over towards the seafront - popular with drones.

So what gives? Unlikely to be stellar in origin. Nothing could build and shed that kind of energy so rapidly that didn't make the news! Satellite laser ranging? Maybe? Very stellar in appearance though. Not a military grade red or green laser then.

A flare off a Molniya satellite at Apogee? Possible I suppose. And that's my final answer. Imperfect but the best I can do!

Your RIGHT!!, looking in stellarium at the exact time the photo was taken shows satellite GlobalStar M006, it matches the area perfectly, a reflection off of the sun is what happened. Well done to you!

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Posted (edited)
5 hours ago, vlaiv said:

they do both look to be about the same in intensity (or near). This would mean that about equal time of exposure is needed for both

I have no idea what might have caused it, but surely this wouldn't necessarily be true if the star(s) are bright enough to saturate the sensor?

I rather prefer the explanation being a transient movement of the mount. Is it a manually operated barn door tracker? Then again, it's suprising that there is no star streaking, which would mean it would have to move between exposures? Hmm!

Ian

Edited by The Admiral

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2 minutes ago, The Admiral said:

I have no idea what might have caused it, but surely this wouldn't necessarily be true if the star(s) are bright enough to saturate the sensor?

I rather prefer the explanation being a transient movement of the mount. Is it a manually operated barn door tracker?

Ian

Any sort of glitch in tracking would leave a trail. If star is bright enough to saturate sensor - it will leave a trail due to either - slow motion of scope between shift positions, or if jump is very very quick - due to OTA/Lens shake.

 

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11 minutes ago, Arran townsend said:

Your RIGHT!!, looking in stellarium at the exact time the photo was taken shows satellite GlobalStar M006, it matches the area perfectly, a reflection off of the sun is what happened. Well done to you!

After some thought we need to check if it is actually possible that said satellite could possibly caused such "flare". I have certain reservations about it so it is best to do "sanity check".

We would need to calculate angular speed of said satellite - we have basic info on that:

Orbital period: 124.3 minutes (semi major axis - 8252 km)

We would also need resolution of above shots in arc seconds per pixel. We can conclude that flaring object did not move more than one pixels for duration of flare. This will give us maximum total flare time. Next we need to calculate amount of reflected solar photons from flat surface of certain size (we can just make approximate there based on Sun magnitude in Earth orbit and some surface area of reflection common for satellites, or even find exact size of solar panels for that particular satellite). We can model reflection to be 100% without much impact on result.

Then we need to see how much photons will reach aperture on earth (given the distance and aperture size) and integrate for max duration of flare.

I have a feeling it will not be enough to saturate sensor for that brief moment - but it might be.

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Hm, need to retract above comment :D

Here is a screen shot from a paper in either Chinese or Japanese or some other oriental language that uses logograms - certainly one I can't speak or read, but graph is self explanatory I think:

image.png.ca9b59ae6a44ee696486ccf23241eb6b.png

From the graph it looks like GLOBALSTAR M006 is capable of producing brightness of Mag 2 star. That is about x8 brighter than 52 Cyg, so should be able to make same "footprint' in about 2 seconds.

However - that thing just zooms around at about 3'-4'/second, and at 300mm lens, with even large pixels, you still need it inside 5" to make above signature, and that would make flare last at most ~30ms. That is almost 100 fold lower than above 2 seconds - which means it should look like mag 7 star - certainly not saturating.

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1 hour ago, vlaiv said:

Hm, need to retract above comment :D

Here is a screen shot from a paper in either Chinese or Japanese or some other oriental language that uses logograms - certainly one I can't speak or read, but graph is self explanatory I think:

image.png.ca9b59ae6a44ee696486ccf23241eb6b.png

From the graph it looks like GLOBALSTAR M006 is capable of producing brightness of Mag 2 star. That is about x8 brighter than 52 Cyg, so should be able to make same "footprint' in about 2 seconds.

However - that thing just zooms around at about 3'-4'/second, and at 300mm lens, with even large pixels, you still need it inside 5" to make above signature, and that would make flare last at most ~30ms. That is almost 100 fold lower than above 2 seconds - which means it should look like mag 7 star - certainly not saturating.

What do you think the probability of it being this satellite?

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2 hours ago, Arran townsend said:

What do you think the probability of it being this satellite?

I'm not convinced unless there is a flaw in my reasoning / calculation.

It moves really fast - so it should either leave trail - if flare was not almost instant, or it should be fainter if flare was really short - which would make it "stellar" looking.

Do you have exact time of the frame / location - I would like to look up position in Stellarium at the time, but also measure speed that it moved with at the time relative to you (angular / across the sky)?

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My reason for suggesting a Molniya class satellite is that it would have lower angular velocity at apogee, possibly with certain viewer geometry they could appear momentarily stationary?

This Globestar satellite is in a circular orbit so not what I had in mind, but the analysis is still interesting!

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I set my location to Dudley and at time shown at @wxsatuser here is how fast it was moving:

image.png.83e64a4a6f214025fab619a6b0e988f4.png

image.png.c0fcf19cc323f7fab2a2242c616c7980.png

It moves roughly 11'5"/s or 665"/s - now that is seriously fast. If we go by upper bound of 5"/px, and we assume that motion was order of one pixel, that would mean that "flash" lasted less than 7.5ms.

We know that 4.2 mag star saturated in 15 second exposure image. This flash lasted for ~ x2000 less. That would mean that it would need to be roughly x2000 stronger to saturate (this is not quite right as we don't know how much star saturated, but let's go with that).

That would be around 8.25 mags brighter, so it would need to be -4 mag to saturate sensor for such short duration and it does not look like it reaches that bright from a graph that I gave. Also, I don't think that it could flare so short without having brightening and dimming phase before and aft - and that would leave a trace.

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Hahaha, this one is a tough one. I'm now almost confident it was the mentioned satellite.

Just ran astrometry job on image and compared "extra" star position to motion of satellite - and I think it matches extraordinary well :D

If you look at "over exposed" version of the trail, you will see brightening and dimming trail that matches trajectory of that satellite. Very, very interesting that it flared for such a short period of time.

image.png.5d1dfb2248a6aaa677cf9d6d3a46f50e.png

image.png.5974d90311def3da63f9175ea6cfbe59.png

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