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FAQ: Noctilucent Clouds

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#1 Thick_asa_Planck

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Posted 02 July 2005 - 03:14 PM

Hi,

I have learnt so much here on the CN forums and i must say a huge thank you to everyone who has helped me on a wide variety of topics, you know who you are!

Anyway, i've been learning from countless people for a while now, so i thought it was about time i tried to give something back to this lively community.

I'm planning to do a series of simple "FAQ'S" on a variety of visible phenomena, and if it is found useful then i'll do some more.

Alex

#2 Thick_asa_Planck

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Posted 02 July 2005 - 03:44 PM

Noctilucent Clouds

What are they?

Noctilucent clouds are clouds that reside at a much greater altitude than regular clouds, around 80 to 90km. As their name suggests, they seem to glow at night.

What are they made of?

These clouds are widely accepted to be made of very small ice crystals.

Why do they shine?

The tiny ice crystals reflect sunlight when the sun is at a sufficient angle below the horizon, usually in the region of 6 to 12 degrees below.

When is it best to see them?

They are best seen at either dawn or dusk, when the sun is between 6 and 12 degrees below the horizon. NLC's are visible at mid northern latitudes in summer, ie: between the months of June and September, and at mid southern latitudes between November and February approximately.

Where is best to see them?

Noctilucent clouds are greatly favoured by mid-northern and southern latitudes, typically between 50 and 65 degrees north or south of the equator. 57 degrees is arguably the optimum latitude to observe NLC's from, but NLC's can be seen from anywhere in this latitude band. Either side of this latitude boundary, the sun either resides too low below the horizon, or the sky does not get dark enough to see NLC's.

What do they look like?

NLC's are often a noticeable electric blue colour, however, they can vary in colour. They often have a distinct structure, and can either appear as a "whirl", a "wave", a "band" or have no distinct structure.

Where should I look?

Perhaps the best time is looking North or North West about 1 to 2 hours after sunset. Clear skies are necessary, because normal clouds will obscure these much higher NLC's, and they can be confused with normal clouds when they are faint with no structure.

Related Links

http://science.nasa....3/19feb_nlc.htm

Gallery:

http://www.spaceweat...y2005_page1.htm

Happy Hunting!

Alex

#3 Vic Menard

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Posted 02 July 2005 - 06:05 PM

My first view of noctilucent clouds came several years ago from Ocala, FL! The clouds were thin wisps that had an almost serpentine spirographic appearance and were multicolored red to blue, just like sunset colors, against a starry backdrop. They persisted for almost an hour, changing shape and color, growing to a maximum coverage of almost 40-degrees wide and probably 20-degrees tall. The temperature was near freezing when I first noticed the display, an hour or so before the first light of dawn. I discovered later that the clouds themselves were the aerosol remnants of an earlier launch from the Cape.

#4 woman

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Posted 03 July 2005 - 02:36 AM

Thank you for this Alex. I much appreciate the info. Keep it coming.
Take care,
Sarah

#5 Thick_asa_Planck

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Posted 03 July 2005 - 06:56 AM

Wow Vic, that sounds incredible, i have never been fortunate enough to see noctilucent clouds in any colour other than blue.

Sarah: thanks!

Alex :D

#6 lighttrap

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Posted 03 July 2005 - 09:24 AM

Alex,
Thank you for your mini-FAQ contributions. I've added links to both this one on Noctilucent Clouds and the one on Zodiacal Light to the Astro Glossary & FAQ thread that is permanently pinned near the top of this forum, so people will always be able to find them easily.

Thanks,
Mike

#7 Vic Menard

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Posted 03 July 2005 - 10:09 AM

It was one of the most unusual spectacles I've ever seen--wish I had my camera gear with me!

#8 Thick_asa_Planck

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Posted 03 July 2005 - 11:31 AM

No problem Mike - is it OK if i do a few more?

Clear Skies

Alex

#9 Thick_asa_Planck

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Posted 03 July 2005 - 11:33 AM

I'll bet Vic! - when i see odd things in the sky, i don't usually spend time visually studying them, i study them visually only after i've taken pictures. Especially when it's something i've never seen before, i keep thinking "it's gona be gone in a few seconds, better take some pictures before it's too late!"

I used to be a purely visual observer, but i know that i'm turning into an astrophotographer slowly but surely!

Clear Skies

Alex

#10 lighttrap

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Posted 03 July 2005 - 11:41 AM

No problem Mike - is it OK if i do a few more?


By all means! Please Do! I'll link them as I see them. You're helping us out. Eventually, I'd like to get the CN FAQ upgraded, fact checked, and greatly expanded. One step towards that end has recently taken place, and over time, I'd like to see it become a superior repository of astro knowledge. Your contributions will *eventually* get integrated, and I appreciate your efforts.

Thank you,
Mike


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