Starship Asterisk*

http://apod.nasa.gov/apod/ap070705.html

Does anybody know whether (or how) the night-shining clouds are related to auroras?

Not related. Aurora are caused by collisions of charged particles from space striking atoms in the Earth's upper atmosphere. Noctilucent cloud are high altitude clouds that are still in direct sunlight after it has gotten dark on the ground.

can anybody tell me how they can take a picture of a night sky over the north pole on june 11 when the sun does not set over the north pole until 25 september?

There is a black area at the pole indicating that there is no data from there.

Article APOD 2006 July 18 mentionned the possibility of the artificial origin of this (or part of) this clouds.

Are there mentions of this kind of clouds anterior to the beginning of the space exploration (say 1957) ?

planete wrote:Article APOD 2006 July 18 mentionned the possibility of the artificial origin of this (or part of) this clouds.

Are there mentions of this kind of clouds anterior to the beginning of the space exploration (say 1957) ?

They were apparently first observed (well, first recorded observation) by an amateur astronomer in 1885, two years after the enormous Krakatoa volcanic eruption. They mention this in a couple of the articles on NASA's AIM site.

bjmb wrote:can anybody tell me how they can take a picture of a night sky over the north pole on june 11 when the sun does not set over the north pole until 25 september?

I'm pretty certain that the imagers the observatory are using are configured to be sensitive to something specific to the noctilucent clouds (eg. a particular range of frequencies of light that they scatter), allowing it to pick them out against the background of the Earth and other clouds, regardless of whether it's day or night. I tried digging through NASA's AIM website, but couldn't find a single shred of technical information on how the CIPS instrument is actually observing them.

i don't want to put too fine a point on it, and i take it that the guys and ladies at nasa know what they are doing, but the whole area north of 70° (which includes the larger part of greenland and the whole island of nova zembla, directly under the clouds) was bathed in continuous sunshine during the whole month of june, so the least one can say is that the picture creates a misleading impression by being mostly black. i take it that the contours of the land were drawn in, but within 70° there is no "night" and therefore, i'd say, no "night shining clouds". but perhaps my reasoning is wrong?

Well, they're really 'Polar Mesospheric Clouds', but we down here on Earth call them noctilucent clouds because they appear to glow in our night sky. If you're located in the sunlit polar regions, you'll probably not be able to observe them as such, no.

The image is an observation of the noctilucent clouds only; they're not meaning to imply that it's a full-spectrum visible light image of the Earth, with the black areas being dark. They're simply those regions where there are no NLCs or they have no data.

So in other words, those clouds depicted in the image are those that, under the right viewing conditions could/would appear as noctilucent clouds but aren't necessairily being viewed as such from the ground at the time this image was taken.

That seems to be the case BMA, , ,

That they are called by my initials, N.L.C., makes them OK in my book,

Norval

BMAONE23 wrote:So in other words, those clouds depicted in the image are those that, under the right viewing conditions could/would appear as noctilucent clouds but aren't necessairily being viewed as such from the ground at the time this image was taken.

More're'less.

They're at such a high altitude that they'd likely be visible from areas -not- in constant sunlight during the summer (which seems to be the season they primarily form in); they also spread south from the pole. So some of these clouds probably -were- visible as NLCs from the ground.

yes, now i have a clear picture. when they are called "night shining clouds", that is a bit of a misnomer, because they are just as "night-shining" as for instance the moon - they receive their light from the sun, but because they are so very high up in the atmosphere, they can be seen thousands of miles to the south where there is real night - like the picture from sweden july 18, 2006, or the three identical ones july 26, 1999, june 15, 2003 and june 19, 2005. the mystery is not their light, but the fact that they form so high up in the atmosphere. the july 5 picture gave (me) the impression they were shining bright in an ink-black polar sky. thank you all for your help.

bjmb wrote:yes, now i have a clear picture. when they are called "night shining clouds", that is a bit of a misnomer, because they are just as "night-shining" as for instance the moon - they receive their light from the sun, but because they are so very high up in the atmosphere, they can be seen thousands of miles to the south where there is real night...

The NLCs that people see and photograph are mostly quite close to their actual location- probably somewhere between overhead and a few hundred miles away. One thousand miles is about the maximum possible distance they could be, since at that point a cloud 100 km high would be on the local horizon.

In the summer, an hour after sunset, a cloud 100 km overhead can still be in sunlight- it doesn't need to be farther towards the pole.

smitty wrote:Does anybody know whether (or how) the night-shining clouds are related to auroras?

Good question smitty since the altitude of auroras is 50 km to as high as 500 km and NLC’s are at an altitude of 50 to 85 km. It would seem there would be a relationship between these two phenomena since they occupy overlapping altitudes.

Wouldn’t NLC’s occur in both hemispheres like auroras do?

disregard

FieryIce wrote:Wouldn’t NLC’s occur in both hemispheres like auroras do?

To quote the explanation from http://antwrp.gsfc.nasa.gov/apod/ap070705.html

... The clouds form over the poles in the corresponding summer season ...

This would suggest to me that both poles are involved.

bystander wrote:

FieryIce wrote:Wouldn’t NLC’s occur in both hemispheres like auroras do?

To quote the explanation from http://antwrp.gsfc.nasa.gov/apod/ap070705.html

... The clouds form over the poles in the corresponding summer season ...

This would suggest to me that both poles are involved.

Thanks bystander, I had a momentary laps and forgot about that image and the wording.


The science about NLC’s is fascinating. Just imagine if Yellowstone blows it would seed that layer and the layer of ice crystals would grow. That kind of layer would be good at filtering the ultraviolet rays that are so harmful. IMHO this would be a good thing, it would make the earth’s surface temperature more even with less extreme cold or hot temperatures. Contrary to the popular misconception, the more moderate overall temperatures would not be a sweltering greenhouse or a glacial freezer. Wanna take a speculative guess as to where all the glacial melted ocean water is going? Some of the small island local people were concerned with the total loss of their island homelands because of the supposed ocean water level rise as a result of polar melts. Well these people have actually gained land as the shoreline has increase with the lower water level.
Fascinating!


Oh I should add this image and link (edited).


Strange Clouds

FieryIce wrote:

smitty wrote:Does anybody know whether (or how) the night-shining clouds are related to auroras?

Good question smitty since the altitude of auroras is 50 km to as high as 500 km and NLC’s are at an altitude of 50 to 85 km. It would seem there would be a relationship between these two phenomena since they occupy overlapping altitudes.

Not intrinsically. I'm not intending to sound sarcastic here, so I apologize if I do, but the same logic would suggest that there is a relationship between deer and trees since both can be found in the forest. If you were to get specific enough, you could identify links, such as both are living organisms, but nothing substantial.

By the token, NLC's and aurora are related in that both involve the atmosphere and the sun, but the mechanisms are different. NLC's are the result of condensation of water and reflection of sunlight. Aurora are the result of absorption of solar energy and subsequent re-emission in the visible spectrum.

That image is a good illustration of NLC's, by the way.

Yes iamlucky13, that was what I was trying to figure out, one reflects the other absorbs. One is highly charged particles the other is not and both display colours in the visual spectruim.

June 2007, the Space Shuttle crew, International Space Station

That is a resent picture; NASA has a two-page gallery of NLC's.

2004 Noctilucent Cloud Gallery

The NASA THEMIS' constellation line up of 5 satellites along the sun-Earth line should get some very good images of NLC's and the "elusive substorm trigger mechanism".

NASA's THEMIS Mission Launches to Study Geomagnetic Substorms

The EPOD has a nice NLC picture.
To quote:

more frequently in the past 20 years or so

Observed from Hungary.
EPOD

Interesting BBC article and short video about NLC's

Spacecraft chases highest clouds