Sunlight hours

Antarctic twilight

Video transcript

Welcome to Mawson station Antarctica! Now, a lot of my friends have said “you’ve told us the sun goes away for 15 days, but in your photos we see light! Why isn’t it completely dark?” There’s a good answer for that.

We all know that once the sun dips below the horizon, there’s that beautiful period of soft light where the sun is close enough to the horizon that the scattered rays of the sun still illuminate the sky and that’s what’s happening here at Mawson. There’s a long extended period where it’s just below the horizon within six degrees, for maybe about five hours even on the shortest day of the year. And that’s the twilight that we see!

[end transcript]

Expeditioner with camera tripod over shoulder walks in front of rising sun
An expeditioner watches as the sun appears over the horizon at Davis, for the first time in six weeks (Photo: Jeff R)
Crimson sunset at MawsonSunset at Casey RangesA double solar haloTowering sun through the ice-laden atmosphere

How much daylight is there in Antarctica during summer and winter?

As you move closer to the poles, the periods of winter darkness and summer daylight increase. The polar circles (both the Antarctic Circle at 66°34′ S and Arctic Circle at 66°34′ N) mark the latitude beyond which the sun remains completely below the horizon on Midwinter’s Day, and completely above the horizon on Midsummer’s Day.

On Antarctica’s coast, where our stations are located, there are usually a couple of weeks in mid-winter (around 21 June) when the sun does not rise, and a couple of weeks in summer around Christmas when the sun does not set.

Compare the graphs below for Mawson and Davis. Davis is located further south than Mawson, so it gets less sunlight hours during winter. At the poles themselves, the seasonal changes are even more pronounced. 24-hour daylight occurs for several months over summer, while in winter there is complete darkness for several months.

The diagrams below show how the length of day changes as you travel north, from the South Pole to Dome A, Davis, Mawson, Casey, Macquarie Island, Heard Island, and finally, Kingston in Tasmania.

South Pole sunlight chart, showing total darkness around the middle of the year, and full sunlight at the start and end of the year
Dome A sunlight chart, showing days of constant sunlight from October–February, and the short days in the middle of the year: never leaving astronomical twilight
Davis sunlight chart, showing the short days in the middle of the year: never leaving civil twilight
Mawson sunlight chart, showing the short days in the middle of the year (never leaving civil twilight)
Casey sunlight graph, showing very short days in the middle of the year
Macquarie Island sunlight chart, showing significantly shorter days in the middle of the year.
Heard Island sunlight chart, showing significantly shorter days in the middle of the year.
Kingston Tasmania sunlight chart, showing significantly shorter days in the middle of the year. Each day has some amount of ‘true’ day and night.

Definitions

Civil twilight

This occurs after sunset or before sunrise when the centre of the sun is up to 6° below the horizon. At this time, the brightest stars are normally visible. Under good weather conditions, terrestrial objects will still be visible.

Nautical twilight

This occurs when the sun is between 6° and 12° below the horizon. At this time, only the general outlines of ground objects may be visible. The horizon is still visible, even on a moonless night.

Astronomical twilight

This occurs when the sun is between 12° and 18° below the horizon. There is no colour in the sky during astronomical twilight. It is not possible to make out the horizon.