The days are getting shorter. The sun is rising at around 0845 and setting just after 1600. It is fast approaching mid-winter's day. We at Macca will celebrate this important event in the Antarctic calendar on the 22nd of June. For those on my email list - I have sent out a invitation to join us.
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| A beautiful recent sunset |
One of the most spectacular sights here, and anywhere in the world is a aurora. The other night we had a nice aurora
australis, which presented itself directly above the station. Unfortunately my camera was out of action (another story) so was unable to get any images.
The Aurora Australis is not only the name of the ship that transported us here. It is also the name of the natural light display that is sometimes seen in the night sky. Auroras occur mostly in the polar regions and is visible almost every night at, or near, the Antarctic and Arctic Circles (66.5°S and 66.5°N). In the southern hemisphere they are called aurora australis and in the northern hemisphere aurora borealis.
The first picts I took of an aurora were somewhat experimental.
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| March 17th looking SE over Garden Bay around 8:40pm |
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| March 17th looking SW from behind the weather office around 9:40pm |
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| March 17th looking Northwest around 11:30pm |
The activity that creates an aurora starts at the sun. The super hot gases of the sun are made up of electrically charged particles called ions. The ions continuously stream from the sun as the solar wind. Most of the solar wind bypasses the Earth, deflected by the Earth's magnetic field. Without this magnetic field the solar wind would blow away the fragile atmosphere, preventing life.
My second attempt was a bit opportunistic. I was at work, but didn't have a tripod, so improvised with two or three copy paper boxes
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| 4th April at 9:20pm looking southeast from just in front of the weather office |
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| 4th April at 9:30pm from the same spot looking SSE |
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| 4th April at 9:35pm from in front of the weather office looking south |
Some of the ions do however become trapped in a ring-shaped holding area around the planet, a region of the atmosphere called the ionosphere. In the ionosphere, the ions collide with gas atoms and the energy released causes a colourful, glowing light - an aurora.
My third attempt was again while I was working. It is very rare that there is little or no cloud, so when a aurora is spotted my and almost everyone else's camera is at the ready.
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| 14th April at 11pm looking southeast from the weather office |
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| 14th April at 11:05pm from roughly the same spot looking east |
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| 14th April at 11:10pm looking east - curtain effect |
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| 14th April at 11:13pm looking southeast |
The colour of the aurora is dependent on the gas. Oxygen emissions are green or brownish red depending on the amount of energy absorbed. Nitrogen emissions are blue or red; blue if the atom regains an electron after being ionised.
The forth attempt was of an aurora that was by far the strongest we have seen. Hence the multiple photos.
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| 1st May at 6:55pm looking southeast from station compound with Camp Hill in the foreground |
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| 1st May at 7pm looking directly overhead from station compound |
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| 1st May at 7:01pm from station compound looking WSW |
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| 1st May at 7:02 from station compound looking WSW - draping silk curtain effect |
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| 1st May at 7:03pm from station compound looking SW - biology building and flag poles lit up |
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| 1st May at 7:04pm from station compound looking WSW - the fence is to keep the elephant seals out |
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| 1st May at 7:06pm from station compound looking almost west - see the 'big dipper' |
Auroras occur often at Macquarie Island, but as there are, on average annually, 315 days of rain, there is limited opportunities to witness them. We are always on the lookout when the sky clears.
The strength of an aurora has been found to be related to sunspot activity and a stronger solar wind. The aurora in the pictures above occurred in these ideal conditions - clear sky and strong aurora.
The fifth and up until now last attempt was a month later - May was very wet, windy and at times snowy, so not much opportunity to see this special event. After these photos were taken it clouded over a heavy snow fall
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| 1st June 9:24pm from the seismology hut looking east across Garden Bay |
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| 1st June 9:25pm from the seismology hut looking southeast across Garden Bay |
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| 1st June 9:29pm from station compound looking almost due south |
There have been many other optical effects gracing the skies of Macquarie Island. These are called photometeors .....
consist of a number of atmospheric phenomena attributed to the reflection or refraction of visible light in the sky by
liquid water droplets, ice crystals, by the air itself, or by solid particles in the
air, such
as volcanic ash or dust.
I have already shown some of these in previous posts. A fogbow is a photometeor. It is similar to a rainbow, though the water droplets that reflect the light are much smaller.
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| fogbow |
Everyone has seen a rainbow - this is another photometeor. There hasn't been many rainbows sighted at Macca, though I have previously shown a rainbow effect in sea spray whipped up by strong winds.
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| Rainbow effect in the sea spray whipped up by the squally winds |
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| Rainbow effect in the sea spray whipped up by the squally winds |
The following pictures are of the rainbow effect, which I have been taken over the last 20 years
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| Double rainbow - taken at Forth, Tasmania in January 1992 |
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| Double rainbow - Doubleview WA June 1994 |
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| rainbow effect in the sea spray - Aurora Australis somewhere in the Southern Ocean - October 2007 |
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| rainbow - Hobart September 2004 |
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| Double rainbow - Melbourne August 2012 |
Another fascinating optical effect are
Crepuscular Rays - these are rays of sunlight streaming through gaps in cloud, which appear to be radiating from a point in the sky where the sun is located. In fact,
despite seeming to converge at a point, the rays are near-parallel shafts of sunlight, and their apparent convergence is a perspective effect (similar, for example, to the way that parallel railway lines seem to converge at a point in the distance) - Wikipedia.
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| Crepuscular rays from Bauer Bay |
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| Crepuscular rays over Handspike Point |
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| Crepuscular rays off West Beach, near station |
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| Crepuscular rays off West Beach, near station |
The following are images of crepuscular rays taken over the last decade. Sometimes these rays are referred to as "The fingers of God"
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| Crepuscular rays - Hobart March 2003 |
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| Crepuscular rays from Rottnest Island WA |
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| Crepuscular rays - West Hobart |
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| Crepuscular rays |
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| Crepuscular rays |
When a
halo is seen around the sun it indicates a layer of high cloud. sunlight (or moonlight) is refracted and reflected in ice particles (crystals). Also seen at low levels in very cold air where ice crystals (diamond dust) have formed.
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| Halo seen from the Aurora Australis |
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| Halo at Casey Station Antarctica |
I have a couple of images of irisation - multiple mixed colour iridescence caused by sunlight dfracted through cloud.
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| Irisation in middle level cloud between Hobart and Launceston |
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| Irisation in middle level cloud in between cumulonimbus clouds |
This last image - I'm not sure what the photometeor is called. Can someone identify it? Someone suggested it was a sun dog.
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| Colour at the edge with the sun behind cloud in the bottom right |
Until next time. Happy Mid-Winter....
nice post Barry, the photometeor part reminds me of my similar post http://rivieraofthesouth.wordpress.com/2013/03/31/summer-skies/
ReplyDeleteAbout your last photo, it looks very much like a sundog (there's an example half way down in my post), although where it appears in relation to the sun is key. It should be where the halo edge is and I've only seen it at the same level (horizontal) as the sun.
cheers
Nick