April, 2004....J. Dana Hrubes...updated April 30, 2004 , 1212 GMT

Aurora Australis reflecting off the dome at the South Pole April 20th

April at the Pole - the light show in the sky begins

April is the month the pole transitions through civil twilight (sun is 0o-6o below the horizon), nautical twilight (sun is 6o-12o below the horizon), astronomical twilight (sun is 12o-18o below the horizon) and then official total darkness around the end of April. You can see a faint glow on the horizon through much of the month of April when the horizon is very clear. This glow rotates around the horizon every 24 hours. In average conditions or when there are clouds, this glow is often not perceptible and the sky appears totally dark after about the second week of April.  early April twilight    dome on april 1st         twilight under new station      south pole twilight     

During early April we also experienced many windy days with poor visibility.    flags to nowhere       snow covered SETI telescope tower       The back door to my Cusp lab is getting harder and harder to keep clear now that is is about 40 feet below the Antarctic plateau now. It requires a great deal of back breaking work.     Cusp back door after several windy days       door shoveled out      ice steps to warmth   from inside out      The dome entrance also gets drifted in now that it is not being dug out any more     drifted dome entrance      dome entrance     looking up from dome exit    And finally after walking almost a mile to the VLF beacon building each day I frequently find a huge drift to dig out just to get in the building     VLF beacon drift  

In early April we had some beautiful days with very clear skies, just a last hint of orange glint of twilight on the horizon where the sun is and temperatures around -80 F, winds...8-10 kts. The auroras were just starting to be visible then. I am able to usually tell when there is an aurora, because I set up some oscilloscopes and have my VLF receiver with an audio monitor so I can constantly monitor VLF and magnetic field signals on the oscilloscopes and listen for the sound of auroral hiss.... When I see and hear the correct signals, I usually check outside to make sure there is an aurora then I make an aurora alert on the station wide PA system.

It is interesting here because in mid April, during nautical twilight, you can just see the last hints of a glow on the horizon as that glow moves around you 360 degrees a day. Where you see the faint glow is where it is about noon on that global meridian. For example, if you see the faint glow at approximately the 0 degree meridian then you know that it is noon on the Greenwich meridian (0 degrees) in England and midnight opposite that, at 180 degrees, or somewhere over the pacific.

The moon is interesting too. It is up for two weeks and then down for two weeks. You can figure out why by taking a couple of balls and drawing on a rotational axis, then incline the "earth" ball about 23 degrees from the horizontal or what would represent the ecliptic plane (orbital plane of the planets around the sun) and visualize yourself at the south pole and look at the moon, the other ball as it rotates about the earth in about 28 days or four weeks. The orbit of the moon about the earth is a few degrees off the ecliptic plane, so when the moon comes up here it spirals up for a week to a 23 degrees plus or minus a few degrees and then spirals down for a week, then it is gone for two weeks.

Also, you can visualize the moon phases really well here when it is twilight and you can see the glow of the sun below the horizon. When moon is full, the brightest part of twilight (or sun below the horizon) is exactly 180 degress across the horizon from the moon. When the moon is at the first quarter or last quarter, the brightest part of twilight (or sun below the horizon) is either 90 clockwise or counter clockwise from the moon. When the moon is new, the glow is exactly under the moon. This phenomenon is now gone as twilight is about over at the end of April.

  Panorama of the South Pole on April 6, during civil twilight. The first moonrise after sunset is always a full moon.  (scroll page to the right to see entire panorama)

By late April the moon set and it was quite dark. The auroras and stars are now beautiful, weather permitting. Photos of aurora are difficult to take not to mention the frozen fingers and cameras and most photos don't even come close to the beautiful visual experience you get when you are really there, but there are a few shown here.     aurora1     aurora2    aurora3     aurora4     aurora5    aurora6   

And finally, the south pole has a winter band this year and I am the drummer. It is really great fun to play again after 33 years. We are trying to have a gig about once a month up in the new galley. We play mostly rock and roll from the 1960's up to some current tunes.  The band's name for the next gig is "The Dana Hrubes Comeback Project"   (not my idea)     the band from the first gig     the rebirth of a drummer from the late 1960's      drummer     

NEXT MONTH:   The darkness continues and temperatures continue to drop

       A Real-Time Photo of South Pole Station as Seen from the ARO Building (live when satellite is up)

           A Comprehensive South Pole Web Site by Bill Spindler

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