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Astrophotography and Sketching >> DSLR & Digital Camera Astro Imaging & Processing

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Eor312
member


Reged: 01/20/12

Loc: La Vergne, TN
Did I capture a corkscrew meteor? new
      #5527635 - 11/19/12 10:28 AM

Taken approx. 0000 2012-11-17 UTC looking southeast from near Nashville, TN.

Taken with a nEOS 1100D, unmodified, Canon EF 50mm f/1.8 lens, unguided, single 10s exposure. No processing other than conversion from raw and resizing.



Larger version here

I was well away from the camera/tripod at the time, nobody else present or near it. Tripod was set up in the yard, not on a hard surface.

No guidance was being used, so nothing could have introduced an oscillation that I can think of. I don't see any suggestion of vibration in the stars, and there was nothing near by that i can think of that would produce a very high frequency/low amplitude wave like that.

I note definite similarities to Jimmy Westlake's APOTD from 2/2/2005



I know it would be unusual to have captured the phenomenon, so I'm being cautiously optimistic here.

Commentary and insights please?


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fmhill
sage


Reged: 07/17/12

Loc: Cape Cod, Massachusetts, USA
Re: Did I capture a corkscrew meteor? new [Re: Eor312]
      #5527721 - 11/19/12 11:15 AM

I do not believe the trail is bright enough to be a meteor, I would guess it is either a spin stabilized satellite or possibly a rotating piece of space junk...

Given my choice of the two, I would say it is most likely a spin stabilized satellite which are quite common...


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Al8236
Pooh-Bah
*****

Reged: 08/18/10

Loc: 48.9173N 122.1390W
Re: Did I capture a corkscrew meteor? new [Re: fmhill]
      #5527736 - 11/19/12 11:22 AM

I'm going to say vibration from some where, The oscillation looks to be about equal to and the same direction as the elongation in your stars.
Just my thoughts!

Edited by Al8236 (11/19/12 11:24 AM)


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Eor312
member


Reged: 01/20/12

Loc: La Vergne, TN
Re: Did I capture a corkscrew meteor? new [Re: fmhill]
      #5527780 - 11/19/12 11:48 AM

Quote:


I do not believe the trail is bright enough to be a meteor, I would guess it is either a spin stabilized satellite or possibly a rotating piece of space junk...

Given my choice of the two, I would say it is most likely a spin stabilized satellite which are quite common...




That has been suggested elsewhere, and general consensus is that a spin stabilized satellite might show a variance in reflection, but not path.

Tumbling piece of space junk is worth consideration, though an out of control, tumbling hunk of solid, entering the atmosphere and burning up...well...now we're just debating composition, right?


Quote:


I'm going to say vibration from some where, The oscillation looks to be about equal to and the same direction as the elongation in your stars.





I understand what you're asserting, but I have two objections to that conclusion. Please understand, I'm certainly not saying you're wrong...you may well be right. I simply don't see how that idea answers the following:

1) The stars appear elongated in the direction of sidereal movement (as they should for an unguided 10s exposure, of course)...which is / in this particular photo.

The object was also moving in the / direction.

Yet, displacement from that path occurs nearly horizontally, like - Note, in fact, the very distinct "stair step" signature at the lower left end of the trail.

In other words...the object periodically displays movement on an axis quite far off the direction of star movement.

2) The object's path is not of a consistent amplitude. It appears to deviate further from its line of travel at some points than it does from others. A vibration would most likely be consistent in amplitude.

3) If it's vibration, it is very high frequency, but very low amplitude. Given the rate that a meteor (or any other object I'm likely to have caught here) is going to me moving, there's quite a few oscillations there in a short period of time...high frequency.

Yet, the displacement is rather small...low amplitude.

===============

Again...certainly not insisting that it's not vibration...merely that some fairly specific traits of the image make it an 'unusual' source of vibration at least...one that would require a fairly specific explanation to convince me I think.


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Tonk
Postmaster
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Reged: 08/19/04

Loc: Leeds, UK, 54N
Re: Did I capture a corkscrew meteor? [Re: Eor312]
      #5529358 - 11/20/12 04:14 AM

Quote:

do not believe the trail is bright enough to be a meteor




How on earth do you come to that conclusion??? Meteors come in all possible brightnesses due principly size and secondly velocity. Is it really impossible to have a 8th mag meteor?

Quote:

..... I understand what you're asserting, but I have two objections to that conclusion ....






Actually what is being observed fits perfectly with a sporadic damped oscillation caused by "stiction" in the gear train (needs cleaniung and relubrication).

Quote:

) The stars appear elongated in the direction of sidereal movement (as they should for an unguided 10s exposure, of course)...which is / in this particular photo.

The object was also moving in the / direction.

Yet, displacement from that path occurs nearly horizontally, like - Note, in fact, the very distinct "stair step" signature at the lower left end of the trail.




I disagree - the asymmetric wave shape in the objects diagonal trail is wholely consistent with a vibration in the direction of the elongated stars - assuming the object was moving at a near constant velocity. I've just done the experiment drawing a diagonal line across a piece of oscillating paper.


Quote:

A vibration would most likely be consistent in amplitude




No reason why this should be likely at all - especially if it iniated by a pulse - e.g. a momentary instance of friction - a small spec of dirt in on gear teeth initiate this behaviour for example.

Quote:

If it's vibration, it is very high frequency, but very low amplitude. Given the rate that a meteor (or any other object I'm likely to have caught here) is going to me moving, there's quite a few oscillations there in a short period of time...high frequency.




This isn't an objection - its just an observed fact that supports the assertion that is a momentary vibration

Yes the observed trace could (but not necessarily) be a high frequency vibration with very low amplitude with a pulse decay signature. My mount had this trouble (stiction) and I was only able to see the true picture when a sattelite traced through the image operating as a convenient oscilloscope . The key signatude is the observation that the amplitude of the star elongation matches the maximum component amplitude of the oscillating satelite/meteor trail. Once I saw that vibration signature (very similar to the above) a gear strip down and relubrication cured the problem. The main observed problem being the presence of elongated stars no matter how well polar aligned due to the stiction source of vibration

Its interesting that the Jimmy Westlake image has been attributed that way as the image could also be interpreted as caused by stiction - the elongated star signature is also present and the amplitude of the star elongation is very very close to the component amplitude in the meteor trail. There is no information supplied by APOD that this possibility was eliminated - for example by two different observers of the same object using different equipment. Jury is out on that one AFAIC


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Eor312
member


Reged: 01/20/12

Loc: La Vergne, TN
Re: Did I capture a corkscrew meteor? new [Re: Tonk]
      #5529537 - 11/20/12 07:53 AM

Quote:

Actually what is being observed fits perfectly with a sporadic damped oscillation caused by "stiction" in the gear train (needs cleaniung and relubrication).






Tonk, I appreciate your fairly detailed analysis that followed this statement.

However, as you'll note from the OP...no gear train was involved. All of your statements regarding the means by which a motorized mount may have created such an image are quite true...but I wasn't using one.

Camera and tripod only.

I was well away from the setup.

Nobody else was present.

Tripod was placed firmly on soft earth, in the yard.

Quote:


Its interesting that the Jimmy Westlake image has been attributed that way as the image could also be interpreted as caused by stiction - the elongated star signature is also present and the amplitude of the star elongation is very very close to the component amplitude in the meteor trail. There is no information supplied by APOD that this possibility was eliminated - for example by two different observers of the same object using different equipment. Jury is out on that one AFAIC





Unless we wish to perform all experiments on all topics ourselves, at some point we must acknowledge an authoritative source on any given topic.

When it comes to meteors, I'll accept NASA as an authoritative source.

NASA posted the image as an example of a corkscrew meteor.

Jury has spoken, AFAIC.

Edited by Eor312 (11/20/12 07:55 AM)


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Tonk
Postmaster
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Reged: 08/19/04

Loc: Leeds, UK, 54N
Re: Did I capture a corkscrew meteor? new [Re: Eor312]
      #5529675 - 11/20/12 09:39 AM

OK no problem - my mistake. You can still get a pulse induced vibration from wind so don't discount this.

Quote:

When it comes to meteors, I'll accept NASA as an authoritative source.




I have to chuckle at this - sorry. Having had 2 APODs myself the "authority" was based off my own write ups I submitted so please don't believe that NASA have gone to the trouble to be totally authoritive on the subject.


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