Solstice – Reprise

Posted on 2013-12-21 by arjaybe

Credit TJP Finn – CC-BY-SA

In Ireland there is a stone structure called Newgrange which has been dated to more than 5,000 years before present. This megalith – literally, big stone thing – is built in a circle, like its famous English cousin, Stonehenge. Both of them are built so as to mark the position of the Sun precisely at winter solstice. Newgrange is a few centuries older than Stonehenge, but they served much the same purpose: to provide a place where people could monitor and probably celebrate the passing of the solstice.

To mark the Solstice, which is just about now by my clock, I’m going to point to a well-received earlier post on the subject. To return to the adventures of Thud, son of Thog, here is Solstice.

rjb

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Sprites

Posted on 2013-12-09 by arjaybe

Image credit - Abestrobi - CC-BY-SA

Image credit – Abestrobi – CC-BY-SA

Cloud of the Day – Sprites

Another non-cloud cloud of the day, sprites are electrical phenomena. They emanate upward from the tops of thunderclouds, as lightning plays around the bottoms. Sprites weren’t caught on film before 1989, and only seriously pursued since then. With intense sprite hunting, and especially with the excellent view from the International Space Station, the database is growing.

image credit - NSF

image credit – NSF

image credit - NSF

image credit – NSF

The National Science Foundation article of 2009 referred to both red and blue sprites, but by 2013 they’d been separated into (red) sprites and blue jets. They’re part of a group of atmospheric phenomena called transient luminous events (TLE) which include, yes, elves. Scientists can be so whimsical.

Sprites last for a very short time – about a thousandth of a second. Their elusive and fleeting nature is what led to their name. They’re big, though. They extend about ten times as far above the cloud tops as lightning does below the bottoms, and they can span hundreds of kilometers. They are also unlike lightning in that they are composed of cold plasma, rather than hot. Nevertheless, we hope there is no precipitation.

rjb

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Aurora

Posted on 2013-12-01 by arjaybe

Photo credit - Deven Stross CC-BY-NC-ND

Photo credit – Deven Stross CC-BY-NC-ND

Cloud of the Day – Aurora

Aurora is not clouds. Clouds can’t form in the tenuous wisps of atmosphere found at the heights, approximately 90 – 1,000 kilometers, where aurora occurs. Therefore, it is wrong for me to call aurora the cloud of the day. Naughty me. It’s a meteorological phenomenon, and it’s beautiful. I’ll call it the cloud of the day if I want.

Photo credit - Alan C Tough

Photo credit – Alan C Tough

Photo credit - Andia Frh

Photo credit – Andia Frh

The Northern Lights, aurora borealis, were named in 1621 by Pierre Gassendi, a French scientist, priest and philosopher. Boreas was the Greek name for the north wind, and Aurora was the Roman goddess of the dawn. The Northern Lights are mirrored around the south pole by aurora australis, the Southern Lights.

Photo credit - 14jbella Click image for huge poster

Photo credit – 14jbella
Click image for huge poster

Photo credit - John Freddy

Photo credit – John Freddy

The aurorae work on the same principle as a neon lamp. Energized atoms release the excess energy as photons of light. In a neon lamp, the atoms are energized by electricity. In aurorae, nitrogen and oxygen atoms are energized by the solar particles that are trapped and funneled into the upper atmosphere by Earth’s magnetic field. When intense enough to be more than a whitish glow, the most common colors are green from oxygen and red from nitrogen. Other colors result from mixing of the main colors, or from variations in the excitation-release mechanism. For example, the rare blue that sometimes comes from nitrogen.

Photo credit - Aaron Kaase - Public domain

Photo credit – Aaron Kaase – Public domain

Although it might be interesting, there is no precipitation from aurora.

rjb

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