One of the issues about NLC are the source of particles which form the condensation nucleii. Often they are quoted as possibly meteoric, I have often wondered if the source may be extra terrestrial but particles which settle into our atmosphere from the vast zodiacal dust cloud in which the Earth is bathed rather than the remains of meteors themselves. The picture of the Zodiacal light was taken last week when I was observing from La Palma. It's 2x5mins at iso 800 using a 8mm lens.
PS the image has now been changed as I uploaded the wrong one.
I wonder if another contributary source of the condensation nuclei could be from microscopic pieces of space junk - I was reading somewhere recently about the exponential rise of this in orbit around the earth. Whilst primarily the article (and I can't for the life of me remember where I read it) was concerning itself with larger pieces of spacejunk and the inherent danger of collision with the space station / satellites etc, I figure for all those larger bits there must be a host of smaller, microscopic, pieces floating around, Maybe these, like zodiacal dust could also contribute?
Am I right is saying that NLC's have increased in frequency over recent years / decades (or have we just been observing them more?) - if there is a rise in frequency could this be married up with the increase in space junk?
I don't know? I was just feeling philisophical after reading your thread Bill...
That's exactly what I believe are the source of NLCs Bill, to me this is the most logical explanation. Excellent image by the way!.
Bill or Tom might know the answer to that one regarding NLC frequency. They do seem to be becoming more widespread, more frequent, and dropping to lower lats than usual although this could be biased by the growing interest in this field over the years so more observers are watching/reporting them. If I recall correctly this point was made last year and Bill said the observational data did not support this?.
It still only a case of "might" be increasing. As, since there are lot's of people looking for them now because they are pretty to photograph, there are oodles of reports. Separating this from a true increase is very difficult. For the 2006 NLC meeting that I organised, for a bit of amusement I tried fitting different curves to the data that I got from Tom's reports spanning 1996 to 2005 and depending on just exactly how the "averages" were averaged I could get the lines to go up or down. All perfectly justifiable mathematically! It will take years to ensure that all the variables can be accounted for. Looking back a data from the 60's shows that NLC's were visible on just as many nights as they are currently visible. The issue I think I raised was regarding the brightness, not frequency as potentially being more important. This is related to particle density and condensed particle size, now THAT'S a different story... The only thing for sure is that the wee bits have got to come from above OR below!
Not really related but a couple of hours after I took the zodiacal light picture I took this one which I've just got around to processing. This is the galactic centre (the brightest bit to the right) rising over the observatory. The brightest "star" is Jupiter.
Intersting reply there John. I was in pure speculation mode when I suggested it so it's always good to have some hard data brought into a discussion. If the sizes you quote pretty much rules out micro-space junk how does the size range for observed NLC condensation nuclei correlate with the size range distribution for Zodiacal particles? Anybody know?
I've had a peruse around the web before to see what I could come up with, and either i'm looking in the wrong places for the info or we've hit a grey area.
I'm not an expert on the physics involved, but if NLC condensation nuclei are smaller particles than those associated with the particles responsible for producing the visible reflected light associated with Zodiacal Light, I wonder if anyone has tried looking at the Zodiacal Light in different wavelengths - eg UV or IR. If smaller Zodiacal particles exist then might it be the case they are visible in other wavelengths?
That's a very astute point! Analysis of polarisation studies indicate NLC particle sizes are around 100nm (depending on whether they are assumed to be spherical or elongated.) The colour of the Zodiacal light is almost the same as the sun indicating much larger size, typically assumed to be around the 10 micron size. So it would seem unlikely that the dust which forms the bulk of the Zodiacal light scattering particles could form NLC nucleii but it's a numbers game. There is in all likely-hood a distribution of sizes from teeny weeny to huge on a relative scale. We are cruising around in a sea of stuff. If the right sort of stuff gets to where it's just the right size to have an effect then an effect there will be. No matter how small the probability is. Forbidden condensation states... Maybe NLC are just quantum meteorology, now there's a great title for a PhD!!!