There's a buzz this summer in the Astronomy/Atmospheric communities about a little-understood atmospheric phenomena called "Noctilucent Clouds". For some reason, this summer has had an outpouring of sightings. With some keen observation and some timing, you can see and photograph these for yourself.

I'll let the fine folks at NASA explain what they suspect they are, but for you
and I, they are a chance to see a fleeting and rare look at clouds that form extremely high in the Earth's tenuous atmosphere. In fact, they're so faint,
only the setting sun, an hour to 90 minutes after sunset can reveal them, and even then, there is no guarantee of a sighting!
The clouds are so interesting, that NASA/JPL found the money to fund the AIM Mission.

So what does this mean to you and I?

If you live in around or above 50th parallel you have the best chance of seeing them, but 2007 has heralded a large number of sightings from the 45th parallel and lower. I live at 48° and I've seen them on 4 occasions this summer, for the first time ever, and that's not with a lack of trying in previous years.

So how do you spot them?

First of all you want an evening with the clearest skies possible, especially on the western horizon. Clouds, especially Cirrus clouds may mask or even emulate them. A good time to start looking for them is 45 minutes after sunset. They are usually confined to within 45 degrees of the horizon; roughly two hands extended at arms length from the horizon. Unlike normal clouds at sunset which appear dark and tinted orange from the sun, NLCs appear to be an unmistakable light neon blue. They will appear bright when the sun no long illuminates regular clouds because it has dipped too far below the horizon to illuminate them. They will appear as delicate, whispy clouds, very much like cirrus clouds, often with wave-like appearances.

If you suspect you're seeing the light neon blue of Noctilucent Clouds, I have found that the best way to confirm it is with a digital camera. A digital camera, with a longer exposure, will able to tell you if what you are seeing are indeed NLCs or not. If you live in an urban or suburban area, regular clouds will appear to be illuminated from below, which may appear like NLCs.

Camera Settings

I use a Canon 10D, with a 17-40mm F4L lens for NLCs. I have found that in twilight, at ISO100, f/4, an exposure of 8-15 seconds is enough to capture NLCs. Like regular clouds, NLCs are moving and dynamic, so exposures any longer might blur these delicate features. But these guidelines will vary for you and your lens. Experiment and find the right setting. I would avoid a combination of ISO and f-stop that yields an exposure of longer than 20 seconds, so experiment with what settings work for you and your lens. Wide angle and telephoto lenses are both great. Wide angle for capturing the overall appearance, or zoom in to capture details near the horizon.

Don't feel too rushed, either. The phenomena can last anywhere from 15 to 45 minutes, in extreme northern/southern latitudes it can last 90 minutes or longer. Urban or rural locations are both fine, they're bright enough to capture if you can avoid bright foreground lighting (street lamps, etc). But for a but of flair, a dramatic foreground object will enhance the photo: a church silhouette, a lighthouse or a calm lake or pond. Foreground objects will help give the viewer a sense of the scale of NLCs. I would classify these events, for most mid-latitude folks (45-55 degrees) about as rare as the Aurora Borealis, and very similar to photograph om technique. Remember, exposures that are too long will lose finer details of the Noctilucent Clouds..

Are they NLCs or are they regular clouds?

In most urban/suburban environments, clouds illuminated from below will turn the bottom of clouds a hue of orange from the wide-spread use of mercury vapor lamps. NLCs will never have this tint in a photographic exposure. So if you see any sort of yellow-orange hue in what you suspect are NLCs, it is most likely regular clouds.

First Noctilucent Cloud I'd ever viewer, June 19, 2007

Gallery: June 19, 2007

Despite being at the right time, these are NOT NLC's. They appeared to be, but a long exposure revealed their orange/pink tint.
Second appearance of NLCs in my area, July 3, 2007. Notice the wavy details close to the horizon.

Gallery: July 3, 2007

Even when conditions are right, you can get false positives. Normal clouds appear orange, yet this cloud (top) appeared bluish. I spect that despite its apperance, its is a regular cirrus cloud. It was too far from the horizon for it to be an NLC but too high up to be tinted orange by city lights.

Gallery: July 3, 2007