Spotting NLC

[heaven31]

Is there any way of knowing for sure that what I'm seeing is NLC?
I look every night that it's clear but I'm not always sure if I'm really seeing them or not lol.

Jo x

[thundergod]

Same here Jo.I have noticed the northern sky at times brighter than other parts and was wondering if it was a NLC display.I recall last years as a vivid herring bone shape but so far I havent seen that yet this year.

[tmcewan]

Hi Jo,

When you see a bright and strong display you'll know for sure as it has a very distinctive colour, texture and structure. Correctly identifying faint, diffuse NLC's is more difficult especially in moonlight or when haze or thin patches of weather (tropospheric) cloud are present. Training the 'NLC' with binoculars can be helpful as they almost always reveal more detail in the NLC structure (they can even reveal finer detail in NLC veils) but not in tropospheric cloud. Watch out for horizontal bands of haze or thin tropospheric cloud near the northern horizon - this can often look like NLC when the bright twilight background shines through the thin fringes of the cloud. Once you have the experience of observing a conspicuous NLC you'll then find it easy to correctly identify further displays. Good luck with your observations!

Tom

[heaven31]

Thanks Tom

When I saw my first and only display last year I did know for sure that it was NLC as it was very bright blueish white and as thundergod said, it had a very distictive herringbone structure to it and also ripples that looked like sand on the beach. I had only read about NLC several weeks before that on spaceweather.com then searched the internet to find more about them.

Since then I've had my loft converted (not for the purpose of observing lol) so now I've got a pretty good view of the sky from my bedroom window. I'd drive out to darker places to try and view them but i can never find anyone else with an interest in them toi come with me lol. My husband thinks I'm nuts being interested in stuff like this and would rather be tucked up in bed than sitting on a dark field somewhere looking at the sky

Thanks again

Jo x

[martinastro]

Hi Joe and Stuart.

From my own experience, for what it is worth, the first sign of possible NLC forming may be the presence of a brightening of the twilight sky in the north or north west (in evening) near the horizon. This is especially so when large bright displays are forming. If you have an obstructed horizon you may see an enhanced blue glow to the sky which looks like a low surface brightness blue auroral band above trees and rooftops. Anyone who is a regular observer will notice this immediately and will make note of the 'something wrong with sky appearance' and understand it as a pre cursor to a developing NLC display.

The complex structured displays which you seen before are unmistakable (and confused with aurora by members of the public) but the fainter (brightness type 1 or 2) Veil types can be much more difficult to spot due to their diffuse/soft or low surface brightness nature. Faint Veils often look similar to a glowing ghostly white fog or mist along the horizon often with a fainter blue (or even subtle green) colour most prominent at the display's top. A suitable exposure with a digital camera will capture it has a white glow. Binoculars may help with this detection. Also the profile of the display may help determine its nature. Often after sunset a low Veil will be at its highest then toward or after midnight it will drop in height as the Sun reaches its lowest position during the night. At this time the Veil will stand out with better contrast against the darker background sky. Before dawn the NLCs will brighten again and grow higher in altitude as the Sun begins to rise again. The NLCs will vanish when the bright twilight washes them from the sky. I hope this is of some help?

To help with brightness and structure identification check out the link below which is an article on my own website with images to help with this area. (if you don't mindTom)...

www.nightskyhunter.com/Noctilucent%20Clouds.html

For eg: here is an image I took in 2005 with a bright pre dawn NLC display and the waning crescent Moon with Earthshine. You can see that there is complex structure here but if you imagine the curls and bands removed from the image until all you can see is the blue-white background glow of the display then this would be a good example of a bright Veil NLC display. This image was taken hand held with an ordinary digital camera with a 2 second exposure (night mode) at ISO400. You remember that night Conor?

www.nightskyhunter.com/NLC%2063-63.html

[thundergod]

Thank you Tom and Martin for your advice on how to spot them.The horizon is not visible from my house but for the last few weeks I have seen the bright glow in the northern sky.
I can get to a better vantage point within 5 minutes,so the next time I see this then I will have a drive and take a look.

[John Murrell]

According to the Observing Guide for NLCs the light from them should be strongly horizontally polarised so their appearance should differ as the polarizing filter is rotated.

The disadvantage is that the polarising filter reduces the brightness.

Has anyone tried this ?

If so does it work and does it help ?

Photographs with the polariser Horizontal & Vertical would be interesting. (How do you detect which way your polariser is )

[martinastro]

I have never used one before John so I couldn't help you there but maybe someone else has? There is an interesting section on the subject provided by Tom on the other thread - a link to a pdf doc detailing a NLC observing guide by Dave Gavine. It is a good read and well worth checking out.

www.iugg.org/IAGA/iaga_pages/pdf/ONC_Sep06.pdf