In Antarctica, the summertime sun never sets. It is perpetual day. Instead of a ducking beneath the horizon, the sun circumscribes the sky every 24 hours. Due to our latitude near south 86 degrees, the sun never gets real high or real low. At local noon, the sun elevation is about 27 degrees. At local midnight, the sun elevation is about 19 degrees. This gives a day with perpetual sunset lighting, free from the stark lighting of harsh noon. This is perfect lighting for landscape photography, where contrary to the actual conditions;
everything has this nice warm glow.
In spite of perpetual sun, the day does go through warming and chilling cycles. It is colder in the early morning and warmest in the afternoon. Sometimes, in the afternoon you can see a thin film of liquid water on the surface of the glacier ice. Even though the air temperature might be -20°C, the local temperature next to the glacier could be much warmer. It becomes notably slipperier to walk on.
Solar noon occurs at about local 13:00 (we are on New Zealand time). At this time the sun is approximately due north. This is a handy fact to know since your standard compass does not work well at all. For people who were raised in the northern hemisphere, one instinctively orients your directions based on the sun moving through the southern sky. Here the mid-day sun moves through the northern sky and constantly confuses one's ability to define compass directions. A compass requires that the magnetic field lines be parallel to Earth's surface, a condition that happens everywhere except at high latitudes. The magnetic field lines for Earth converge at the poles and point into the ground. The compass needle thus has a significant downward magnetic force which confuses the needle. Like Captain Sperry's compass in "Pirates of the Caribbean," at high latitudes, the compass needle points in any direction you want. If you hold a compass so that it is perpendicular to Earth, the needle will point into the ground.
The intensity of the sunlight is measured as watts per square meter and sometimes referred to as solar flux. Before the sunlight penetrates our atmosphere, the solar flux is about 1300 watts per square meter. After traveling perpendicular through Earth's atmosphere the solar flux is about 800 watts per square meter. Due to the oblique nature of sunlight at high latitudes, the rays pass through a much greater path in the atmosphere, thus the summertime solar flux is closer to 400 watts per square meter. For converting sunlight into electrical power, this is the best you have to work with. The grand irony is that where you need solar power the most, the intensity is the least.
Living in constant daylight affects a number of human habits. Inside your tent, it is always light. In McMurdo, we were sleeping six to a windowless room in dormitory style. It was handy to have a small flashlight to see things without waking up sleeping bunkies. Out in the field, a flashlight is not needed.
Your tent becomes a live-in solar clock. From inside, the sun projects a diffuse spot on the fabric which fills the role of a clock's hour hand that moves in a great circle around the tent every 24 hours. When the diffuse spot is aligned with the east facing tent pole, it is time to go to work. When the spot is aligned with the door, it is time for lunch. And when this hour hand is in the middle of the far tent wall, it is time to go to bed. Not only is a flashlight not needed, but neither is a tent clock.
Sleeping in constant daylight can be troublesome. What works well for me is to turn my pile earflap sleeping hat around backwards. These pile hats, built like a stocking cap with earflaps and chin strap, are the fabric equivalent to the old motorcycle skull caps. If worn backwards, the once rearward but now forward section of the hat comes down to just below eye level, tastefully masking out most of the light while allowing one to still peek around. Come morning, all one has to do is rotate your hat 180 degrees and you are ready to tackle the world. Like hunger being the best spice, perhaps the most important factor in daylight sleeping is that after a full day's work in -40°C wind chill, one is tired and ready for a good sleep.
On Space Station, you orbit the Earth 16 times every day. This means you see 16 sunrises and sunsets, doled out every 90 minutes. On earth, when the sun sets, it takes about 2 minutes for the solar disk to slip below the horizon. In orbit, it takes 7½ seconds. And being above the atmosphere, when the sun sets (or rises) the change is immediate. There is no twilight.
In Antarctica, the perpetual daylight is a non-intuitive change. You rely on other clues for the passage of the work day and when it is time to sleep. We can control our environment on Space Station to a higher degree than in an Antarctic tent. On Space Station, we place a shutter over the windows when it is time to make things dark. At first this seems mad, to intentionally mask out such beauty. And Earth from space is this blue jewel of Nature that beckons your call. However, a higher calling of Nature trumps any occipital pleasure and like a little boy who only reluctantly acknowledges bed time, one is forced to close the shutter, turning your back on sheer beauty, and sleep in the process.