Antarctica is a landmass defined by seasonal extremes, where the tilt of the Earth’s axis dictates a dramatic shift in sunlight and temperature. Because the continent is located in the Southern Hemisphere, its seasons are reversed compared to those in the north. While the Northern Hemisphere experiences summer, Antarctica heads into a period of profound cold and darkness. The transition into the Antarctic winter is not defined by a single date, but rather by different scientific and natural markers.
Defining the Start of Winter
The question of when winter begins in Antarctica has two distinct answers: astronomical and meteorological. Astronomical winter is tied directly to the Earth’s orbit and tilt, beginning at the winter solstice. In the Southern Hemisphere, this event occurs around June 21st, when the South Pole is tilted farthest away from the sun, resulting in the shortest period of daylight.
Scientists and meteorologists rely on a more practical definition based on temperature cycles. Meteorological winter is defined as the three coldest months of the year: June, July, and August in the Southern Hemisphere. The meteorological start date of June 1st is the convention most frequently used by research stations and climate experts to mark the beginning of their winter season.
The transition to winter conditions often begins even earlier, with initial signs appearing in March as summer ends. For example, the sea ice surrounding the continent typically begins its annual expansion around March, marking a practical shift toward winter conditions. This early onset of freezing conditions provides a gradual entry into the full Antarctic winter.
The Polar Night Phenomenon
The most dramatic aspect of the Antarctic winter is the “polar night,” a period when the sun remains below the horizon for more than 24 consecutive hours. The length of the polar night varies significantly based on a location’s latitude, or its distance from the South Pole.
The Antarctic Circle, located at approximately 66.5 degrees South, marks the northernmost boundary where a 24-hour night can occur, even if only briefly around the solstice. The duration of continuous darkness increases dramatically the closer one travels toward the geographic South Pole. At the Amundsen-Scott South Pole Station, the sun sets around the autumnal equinox in March and does not rise again until the spring equinox in September, resulting in nearly six months of darkness.
Despite the term “polar night,” it is not a period of pitch blackness everywhere across the continent. Areas closer to the Antarctic Circle often experience a prolonged twilight, known as civil or nautical twilight, where the sun is just below the horizon but still provides a noticeable glow. Only locations at the highest latitudes, above roughly 84 degrees South, experience a true “astronomical polar night,” where no light is visible.
Extreme Conditions During Winter
Once the Antarctic winter is fully underway, the physical environment transforms. The lack of sunlight during the polar night allows the landmass to radiate heat into space, driving temperatures to their lowest annual levels. The average winter temperature across the continent is approximately -34.4 degrees Celsius, but inland areas are dramatically colder. The interior of the East Antarctic Plateau regularly records temperatures between -60 and -80 degrees Celsius, making it the coldest place on Earth.
This intense cold drives the massive annual expansion of sea ice around the continent. Sea ice extent typically reaches its maximum in September, covering an area approximately six times larger than its summer minimum. This maximum effectively locks the continent in place, severely limiting access and isolating research stations that remain operational. Wintering personnel, often called “winter-overs,” are self-sufficient and cut off from outside resupply or evacuation for many months due to the impenetrable ice pack and extreme weather.