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© Martin McKenna/Spaceweather
NLC photographed near Dunluce Castle, Co. Antrim (North Coast), N. Ireland on July 9, 2011.
The season for spotting Noctilucent Clouds or the "night-shining" clouds has begun, NASA said in a statement in early July.

Noctilucent Clouds are composed of tiny ice crystals 40 to 100 nanometers wide, which is just the right size to scatter blue wavelengths of sunlight, a NASA scientist explained.

According to NASA, the best time and location to search for these breathtakingly beautiful phenomenon would be between mid-May and the end of August in the northern hemisphere. However, with no explanation yet found, these glowing, mystical clouds have been seen even as far south as Utah and Oregon and Denver, Colorado in the recent years.

Comment: For the possible explanation, read the comment at the end of the article.

Noctilucent Clouds were first observed in 19th century but their appearance has increased over time and are seasonal, appearing most often in late spring and summer every year.

NASA's AIM (Aeronomy of Ice in the Mesosphere) satellite, which was launched in 2007, continues to study the clouds, while scientists strive to know if noctilucent clouds signal climate change.

"They were a high-latitude phenomenon, but in recent years, AIM has spotted the clouds appearing ever lower in latitudes, but just why is not yet known," NASA said.

Noctilucent Clouds first appeared in the nineteenth century, the era of Industrial Revolution; they are spreading in the recent years, which has puzzled scientists to the possible connection of the clouds with weather and climate, it added.

As this "beautiful mystery" refuses to unravel itself, check out some of the startling pictures from Noctilucent Clouds season 2011:

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© NASA/Marek Nikodem
In Poland, noctilucent clouds season is the time of young stork births. Thousands of storks (Ciconia ciconia) arrive in Polish each spring. This photo was captured on June 26, 2011.
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© NASA/Dave Hughes
Dave Hughes photographed the NLCs near Edmonton, Alberta Canada on July 2, 2011.
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© NASA/Adrian Maricic
NLCs on July 3, 2011 in Lock Leven, Fife Scotland.
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© NASA/Adrian Maricic
This image of NLCs was taken by Adrian Maricic at Loch Leven, Fife Scotland on July 2, 2011.
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© Tony George/Spaceweather
NLC photographed in Umatilla, Oregon on July 1, 2011.
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© Alan Dyer/Spaceweather
Noctilucent Clouds near Gleichen, Alberta, Canada on June 6, 2011.
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© Steven Rosenow/Spaceweather
NLC photographed in Potlatch, Washington on July 2, 2011.
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© Aaron Kennedy/Spaceweather
NLC photographed in East Grand Forks, Minesota on July 1, 2011.
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© Aurimas Dirse/Spaceweather
NLC photographed in Vilnius, Lithuania on June 27, 2011.
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© Marek Nikodem/Spaceweather
NLC photographed near Szubin, Poland on June 26, 2011.
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© Renata Arpasova/Spaceweather
NLC photographed in Swindon and Avebury, Wiltshire, UK on June 29, 2011.
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© Alan Dyer/Spaceweather
NLC photographed near Gleichen, Alberta, Canada on June 28, 2011.
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© Dariusz Wierzbicki/Spaceweathe
NLC photographed in Warsaw, Mazovia, Poland on June 26, 2011.
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© John Houghton/Spaceweather
NLC photographed in Newtown Linford, Leicestershire, UK on July 2, 2011.
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© Marek Nikodem/Spaceweather
NLC photographed in Szubin, Poland on July 10, 2011.
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© Mikael Johannesen/Spaceweather
NLC photographed in Hvidovre, Denmark on July 10, 2011.
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© Benjamin Lawlor/Spaceweather
NLC captured in Dublin, Ireland on July 2, 2011.