29
Jan
On January 2010, Per-Arne Mikalsen took several pictures of a vast aurora erupting over the northern Norwegian town of Andenes. In one of the images he noticed a mysterious green parachute-like object hanging with the main aurora….although more research to be done, it appears that the strange object is certainly the result of a lens flare or an auroral reflection from a satellite (this would be a first time!). The full article can be read on the Discovery News at: http://news.discovery.com/space/aurora-mystery-solved.html#view-comments
Nice pics:
Is this a joke?
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For people who are not used of night pictures, I summarized the major points:
1) It is stated is the article :
“Usually such aberrations appear when there is a small and intense source of light in the field of view, or at least so close that the light from it hits the lens [...] That seems not to be the case here.”
You can trace a straight line from the intense light to the caustic. This light (house, center left) is over-saturated. Distance and size of the caustics depends on the optics.
The article deals with that after.
2) The green color is irrelevant: this image has very probably been processed. (the blue channel has probably been attenuated, thus the green is more visible.)
Moreover, I see some red around the caustic.
I tried to do the same processing on some of my personal pictures (another reason to not thrash bad pictures!) and these caustic really appear green like aurora!
Please remember that a digital camera is not a spectrometer. There is an overlapping between the different channels (For the skeptics: I used a spectrometer as an objective for my personal canon EOS 350, so I was able to check that), as for the human eye.
Unfortunately, physicist and astrophysicist are sometimes confused by colors: we often superpose spectral infomation as
different colors. (and for earth auroras, we use narrow band filters, typically in red 630nm and green 557.7nm oxygen forbidden lines when we want to study above ~100km; typical light pollution are then neon lamps, which have strong lines near 630nm)
3) Do you see a caustic when there is an iridium flare?
Typically, a brigh Iridium flare on a photo looks like that:
http://astroti.free.fr/astroti/nimgs/iridium_filante_carca_sm.jpg (sorry, argentic picture)
This kind of auroral pictures are typically 10-30s exposures. During that time, the iridium satellite moves. And it is very unlikely that the caustic created looks like that. Unfortunately, the metadata of the picture don’t give us the exposure time, only that it was processed by photo$.
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If the author of the picture is still not convinced, he should take the same picture, with the same post-processing; but without any aurora!
Anyway, I suggest that this is really a joke, because in the main article, the picture is cut so that you can’t see the bright light, and the real size and position of the caustic.
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To conclude, I suggest to add a “photographic misidentification” section on this very interesting website.
(And why not include the tips to include usable pictures: raw images, image taken in the same conditions…)
Guillaume
See now:
http://www.caelestia.be/andenes.html
First picture of auroral light bouncing off satellite?
on Caelestia website.
Roberto
Bonjour Guillaume,
Excellent Bonne annee 2012, et j” espere que tout va bien de ton cote !
Je pense sousmettre un abstract pour la session Education/Outreach du prochain EGU….
J’ai vu que tu es organisateur cette annee aussi….j”espere que l’on pourra se rencontrer de nouveau…je discutais hier avec mon collegue Norvegien qui etudie le phenomene Hessdalen, et peut-etre qu’il enverra aussi une demande, dans la session sur les lightnings ou sur la tienne…
Je n”ai pas encore cree une partie mis-identifications avec les photograhies, mais c” est une bonne idee et je ferais cela dans le futur proche…
Bonne soiree,
Amities,
Philippe