Friday, August 04, 2006

Nacreous and Noctilucent

No, this isn't Dermatology jargon (at least I hope not!) - these are two of the rarest (and most beautiful) cloud formations.

Did you know that clouds are water? Clouds form from rising air, which gets cooler the higher up it moves. Cool air in a lower atmospheric pressure can't hold as much water, so water condenses into cloud droplets. If the cloud moves higher, the cloud droplets will get together to form water droplets. Water droplets are too heavy to float, so will fall down as rain or snow.

Although there are many cloud types, there are several large categories. "Cirrus" clouds are wispy, "stratus" clouds are flat or layered, and "cumulus" clouds are puffy. (Fog is a cloud with its base on the ground.) Clouds are also named based on what layer of the atmosphere they are located in.

Nacreous clouds (aka Mother-of-Pearl clouds) are beautiful, rare clouds that form under strict conditions: temperatures lower than minus 80 degrees Celsius and only seen at sunrise or sunset.

Noctilucent clouds are clouds that shine at night and form in a very high (85km up) part of the atmosphere.

Stay tuned for... crepuscular rays :)


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