Sunset

We were so lucky this year to be able to see a long and beautiful sunset at the South Pole!  The official sunset occurred at 2:54 PM on March 23 local time.  If the earth did not have an atmosphere, sunset would have occurred about a day earlier, but because of the refraction of light when it hits the atmosphere, we enjoyed one extra day of sunlight, and we will get another extra day of sunlight at sunrise in about six months.  In the days preceding the sunset a thick ice fog shrouded the area, visibility dropped to less than 1/4 mile, and our hopes of seeing the sunset appeared doomed, but then, miraculously, the fog dissolved and cleared the air for a view of a spectacular sunset, my first one since I left New Zealand on Oct 19, and likely my longest ever, lasting a good couple of days.
We set up a 12" telescope in the galley and took turns at the eyepiece to try and see the very elusive green flash.  The green flash is produced by the refraction of light against the atmosphere.  Just like the color of the sun changes to red at sunset, in a phenomenon of reverse mirage, a green band of light can become visible at the top of the setting sun, when the atmospheric conditions are right.  It occurs at all latitudes.  Sailors on the ocean are the most likely to see one.  It is called a flash because it lasts a fraction of a second at mid-latitudes.  Here at the pole, with a sunset lasting days, under the right conditions, the flash lasts several seconds, and it comes and goes for hours at a time.  The right conditions at the South Pole this year occurred in the evening of March 22, and then again in the morning on March 23.  I was lucky to be in the galley for a late dinner around 9 PM on March 22, after spending the afternoon skiing, right at the time when the sun decided to display the green.  I could not see it with my naked eye, but could clearly see it through the telescope.

Christy was able to record the green flash with her camera in the morning of March 23.

In the days preceding the sunset, as the sun revolves lower and lower on the horizon, the shadows get longer and longer, and the plateau changes its appearance hour by hour.  On March 17, it looked like an ocean, with just the top of the sastrugi lightening up like the crest of the waves on rough seas.  As a reference, the tower in the picture is 100 ft (30 mt) tall.

This is the last photo of the sun before a dense ice fog came down and reduced the visibility to less than 1/4 mile threatening to deprive us of the only sunset we were entitled to in more than one year.  I took this photo on March 19 at the end of the skiway, 2.5 miles from the station, where I went on skis.

A steady wind during the following two days blew the ice fog against anything that would stand up against it on the plateau.  This is what the station looked like when the fog started to disappear on March 22.  It looks very wintry, even though, astronomically, this is still summer down here.

There has been a lot of activity in the station around sunset, as we are trying to catch the last few days of daylight and twilight to complete outdoor work, before darkness sets in and makes things much more difficult.  Six of us have been going out to the wasteyard all week long to sort a large amount of construction materials left behind at the end of the summer.  Everything needs to be sorted into what can be re-used, what is recyclable (and we have 22 categories of recycling materials) and what is not recyclable.  In the end everything needs to be taken off the continent, in full respect of the Antarctic Treaty.  We have been working two hours every day in -60 C (-76 F) temperatures before the cold has been forcing us back inside for hot drinks.  We should be able to finish today.  In this photo, taken on March 22, the sun appears as a shade of orange behind the dissolving fog.

As the sun reappeared out of the fog in the evening of March 22, I put on my skis,turned on my MP3 player, and to the tune of Bach's Brandenburg Concert I went back to the end of the skiway for a shot at the sun disappearing beneath the sastrugi.  The orange circle in this photo is sunlight diffused by the remaining fog.  The actual sun is the very brightest last sliver of light right up against the snow.  I will not be able to listen to the Brandenburg concert again without thinking back to this fabulous ski trip.

On March 23, to the tune of Spyro Gyra, a CD that had accompanied me all the way to the AGO site when the sun was the brightest, I went on my last run of the summer to wave good-bye to the sun for the next six months, but at -61 C (-78 F), and with a windchill of -84 C (-120 F), it was a short one: only 2 miles.  A little later, at 1 PM, and just two hours before the official sunset, I went on the roof of the station to take the last photo of the sunset.  Here again, the actual sun is the thin line of bright light closest to the horizon.  The cloud of smoke seen in this photo is from our nearby power plant.

As tradition obliges, we celebrated the sunset with a sumptuous dinner on March 19, the Saturday before sunset.  The menu included Crostini and Baked Shrimp Wrapped in Bacon and Cream Cheese as appetizers, Duck Breast with Mixed Green, Lobster Tail and Beef Tenderloin with a Jack Daniels Demi-Glaze as the entree, three different desserts, and Australian wines.  We set up a long table for the 49 of us, we played some old Billie Holiday songs, and watched the fireplace on large LCD screens while the sun shone its last rays into the room (photo courtesy of Susan).

My contribution to the sunset dinner was the ironing of all the table cloths.  Susan took this photo as I was hard at work in the laundry room.

Now that the sun is down, the science work will take on a new pace.  We have to shut down the solar observations and, in a couple of weeks, at the end of the period of civil twilight, which will occur when the sun reaches 6 degrees below the horizon, we will start turning on the instruments that look at the night sky.  For me this includes two all-sky cameras that record auroras and two high resolution interferometers that measure wind speeds in the mesosphere (that is 100 km above the earth) by Doppler shift of oxygen molecule emissions.  The pyranometer in this photo on the roof of the Atmospheric Research Observatory has been measuring the bightness of the sky all summer long.  The arm on the right of the instrument roates to shadow the sun and remove its contribution from the measurement.  Seen in this picture is also the full moon, which occurred at the same time as the sun was setting.  Yesterday, March 24, we saw Venus for the first time, and we expect the sky to start turning on its stars one at a time over the next few weeks.  The moon and the stars will be the only lights to guide us for the next six months, as we will continue to venture outside for work and for recreation.