Strange streak discussion: 2004 Dec 7 APOD
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BrainChild
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Guest
Re: Unidentified dark line
Nice photo.
I believe that the dark linear feature is almost certainly caused by an aircraft contrail, as Paul Doherty has suggested. I have seen these many times, and they do not require extended camera exposure time if the atmosphere is sufficiently turbid (enough haze present) and is otherwise illuminated by sunlight. The solar geometry (inferred from illuminated clouds in the upper right portion of the photo) appears to support the observed orientation of the shadow, and although the sky region of interest is not shown in this photo it does appear that there are clearer skies in the vicinity of where the contrail would have been (if one were able to pan farther to the left, and then up). The viewing geometry requirements for these phenomena are as Paul indicates...we are effectively observing the cross section of a relatively dark planar object in the sky...recalling that the cross section of a plane is simply a line. The presence of upper level clouds (cirrus) in this photo yields another clue pertaining to the state of upper atmospheric moisture...increased moisture is conducive to contrail formation and persistence (ie, if the atmopshere is too dry, the contrails will evaporate shortly after formation, or not form at all). It makes sense for contrails to last in environments that support their existence and this is why we often see contrails preferentially in the vicinity of naturally occurring cirrus (although the only real requirement in the moisture).
Steven D. Miller, Ph.D.
Naval Research Laboratory
Monterey, CA
I believe that the dark linear feature is almost certainly caused by an aircraft contrail, as Paul Doherty has suggested. I have seen these many times, and they do not require extended camera exposure time if the atmosphere is sufficiently turbid (enough haze present) and is otherwise illuminated by sunlight. The solar geometry (inferred from illuminated clouds in the upper right portion of the photo) appears to support the observed orientation of the shadow, and although the sky region of interest is not shown in this photo it does appear that there are clearer skies in the vicinity of where the contrail would have been (if one were able to pan farther to the left, and then up). The viewing geometry requirements for these phenomena are as Paul indicates...we are effectively observing the cross section of a relatively dark planar object in the sky...recalling that the cross section of a plane is simply a line. The presence of upper level clouds (cirrus) in this photo yields another clue pertaining to the state of upper atmospheric moisture...increased moisture is conducive to contrail formation and persistence (ie, if the atmopshere is too dry, the contrails will evaporate shortly after formation, or not form at all). It makes sense for contrails to last in environments that support their existence and this is why we often see contrails preferentially in the vicinity of naturally occurring cirrus (although the only real requirement in the moisture).
Steven D. Miller, Ph.D.
Naval Research Laboratory
Monterey, CA
pauld@exploratorium.edu wrote:I've seen a similar phenomenon many times before.
Perhaps it is the shadow of a contrail on the air?
The shadow of a contrail falls on hazy air.
Often contrails are straight lines.
When you are inside the shadow looking along it you can see the shadow. Look at right angles and you cannot see the shadow.
When the contrail drifts due to wind, you are no longer inside the shadow and cannot see it.
This is why it is visible only briefly.
Paul Doherty
Senior Staff Scientist
The Exploratorium
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Jason
The streak
If it is a photograph taken with a NON-Digitial camera...
It has been known that sometimes film is creased, ie a defect in that piece of film. The result is a line which can be found on the negative.
If it is digital, I know not.
It has been known that sometimes film is creased, ie a defect in that piece of film. The result is a line which can be found on the negative.
If it is digital, I know not.
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Guest
Re: Unidentified dark line
Care to address how a "contrail" can appear and disappear in 30 seconds?
Anonymous wrote:Nice photo.
I believe that the dark linear feature is almost certainly caused by an aircraft contrail, as Paul Doherty has suggested. I have seen these many times, and they do not require extended camera exposure time if the atmosphere is sufficiently turbid (enough haze present) and is otherwise illuminated by sunlight. The solar geometry (inferred from illuminated clouds in the upper right portion of the photo) appears to support the observed orientation of the shadow, and although the sky region of interest is not shown in this photo it does appear that there are clearer skies in the vicinity of where the contrail would have been (if one were able to pan farther to the left, and then up). The viewing geometry requirements for these phenomena are as Paul indicates...we are effectively observing the cross section of a relatively dark planar object in the sky...recalling that the cross section of a plane is simply a line. The presence of upper level clouds (cirrus) in this photo yields another clue pertaining to the state of upper atmospheric moisture...increased moisture is conducive to contrail formation and persistence (ie, if the atmopshere is too dry, the contrails will evaporate shortly after formation, or not form at all). It makes sense for contrails to last in environments that support their existence and this is why we often see contrails preferentially in the vicinity of naturally occurring cirrus (although the only real requirement in the moisture).
Steven D. Miller, Ph.D.
Naval Research Laboratory
Monterey, CA
pauld@exploratorium.edu wrote:I've seen a similar phenomenon many times before.
Perhaps it is the shadow of a contrail on the air?
The shadow of a contrail falls on hazy air.
Often contrails are straight lines.
When you are inside the shadow looking along it you can see the shadow. Look at right angles and you cannot see the shadow.
When the contrail drifts due to wind, you are no longer inside the shadow and cannot see it.
This is why it is visible only briefly.
Paul Doherty
Senior Staff Scientist
The Exploratorium
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BrainChild
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MarkS
Optical Lens Artifacts
Given the position of the sun in the sky and the angle of the small bright "cloudy" streak, I suspect that the phenomenon is caused by a reflection of sunlight off an object floating in the water. The short, bright streak points directly at the sun, as optical artifacts of a lens do. The long, dark streak may be either a shadow of the original reflection in the atmosphere caused by an irregularity in the reflecting surface of the object in the water, or possibly an anti-reflection in the camera's lens - in essence the optical counterpart to the short, bright streak.
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Guest
Is it really so mysterious? We've seen magic shadows before
http://antwrp.gsfc.nasa.gov/apod/ap010219.html
Perfectly straight streak, emanating from a source of light, the streak is gone as soon as the flash (light source) is gone.
There's a wisp of smoke at the bottom of that pole... So there was an electrical short, eventually the light on that pole blew up, and the flash cast a shadow toward the photographer.
no?
http://antwrp.gsfc.nasa.gov/apod/ap010219.html
Perfectly straight streak, emanating from a source of light, the streak is gone as soon as the flash (light source) is gone.
There's a wisp of smoke at the bottom of that pole... So there was an electrical short, eventually the light on that pole blew up, and the flash cast a shadow toward the photographer.
no?
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Pez
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Guest
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Guest
Re: Unidentified dark line
Anonymous wrote:Care to address how a "contrail" can appear and disappear in 30 seconds?
Actually, this issue was addressed. One issue that was not addressed by the contrail shadow theory was why the bright spot at the end of the shadow looks like a bug. Another unaddressed rebuttal brought against the contrail shadow was that the lighting for a shadow of this angle is very wrong.pauld@exploratorium.edu wrote: When the contrail drifts due to wind, you are no longer inside the shadow and cannot see it.
This is why it is visible only briefly.
--"purplecube"
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Bummer
Or it might be something like this http://www.worldwindcentral.com/view_hotspot.php?id=133, a srceenshot of nasa's worldwind http://learn.arc.nasa.gov/worldwind/, displaying some piece of desert in Victoria.
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Bear
