Side-by-side comparison of the June and December solstices
2022-06-20. People like me who live at mid- and high latitudes experience substantial changes in the lengths of daylight and nighttime between winter and summer. We owe this seasonality in the lengths of day and night to the 23.44° inclination of the axis of rotation of the Earth relative to the ecliptic plane (the plane of Earth’s orbit around the Sun).
The June solstice usually occurs on June 21 but may also occur on June 20. It is the longest day of the year in the northern hemisphere where it is referred to as the summer solstice. It is the shortest day of the year in the southern hemisphere where it is referred to as the winter solstice.
The December solstice usually occurs on December 21 but may also occur on December 22. It is the shortest day of the year in the northern hemisphere where it is referred to as the winter solstice. It is the longest day of the year in the southern hemisphere where it is referred to as the summer solstice.
Days with equal 12-hour daylight and 12-hour nighttime occur simultaneously at all latitudes on the aptly named March and September equinoxes.
I arbitrarily picked the city of Rimouski (48°27’N, 68°32’W), where I live, and the city of Ushuaia (54°48’S, 68°18’W), to illustrate the extent to which the June and December solstices affect received sunlight in Earth’s northern and southern hemispheres. The tiny longitude difference (14′) between Rimouski and Ushuaia is equivalent to slightly less than one minute difference (56 seconds to be precise) between their local solar times.
On the June solstice, the sun lights up the North Pole and all locations situated north of the Arctic Circle for 24 hours. At Rimouski, the Sun reaches a maximum angle of 65° (90° – 48.45° + 23.44° = 64.99°) above the horizon at solar noon, its highest position of the year in the sky. Meanwhile, the South Pole and all locations situated south of the Antarctic Circle go through a 24-hour night. At Ushuaia, the Sun reaches a maximum angle of 12° (90° – 54.8° – 23.44° = 11.8°) above the horizon at solar noon, its lowest position of the year in the sky.
On the December solstice, the North Pole and all locations situated north of the Arctic Circle go through a 24-hour night. At Rimouski, the Sun reaches a maximum angle of 18° (90° – 48.45° – 23.44° = 18.11°) above the horizon at solar noon, its lowest position of the year in the sky. Meanwhile, the Sun lights up the South Pole and all locations situated south of the Antarctic Circle for 24 hours. At Ushuaia, the Sun reaches a maximum angle of 59° (90° – 54.8° + 23.44° = 58.64°) above the horizon at solar noon, its highest position of the year in the sky.
June solstice
On June solstice day, communities like Tromso (Norway) and Tuktoyaktuk (Canada) enjoy 24-hour daylight. Along the Tropic of Cancer, the Sun gradually rises in the morning until it makes a perpendicular angle of 90° with respect to the horizon at solar noon and then descends in the afternoon. At the South Pole conditions for astrophotography are ideal all day!
I produced a fun to watch animation on Vimeo that shows which parts of the Earth are sunlit, minute by minute, during the entire June solstice day.
December solstice
On December solstice day, a person at the South Pole would enjoy 24-hour daylight. Along the Tropic of Capricorn, the Sun gradually rises in the morning until it makes a perpendicular angle of 90° with respect to the horizon at solar noon and then descends in the afternoon. Arctic explorers at the North Pole would experience a 24-hour night.
I produced a fun to watch animation on Vimeo that shows which parts of the Earth are sunlit, minute by minute, during the entire December solstice day.
Side-by-side comparison of the two solstices
Now imagine putting two heat resistant cameras on opposite sides of the Sun. In this thought experiment illustrated below, camera J would film the Earth during 24 hours on June 21. Six months later, camera D would also film the Earth for 24 hours on December 21.
If we were to put side by side the films collected six months apart by camera J and camera D, what would we see? I produced an animation on Vimeo that answers this question. Go watch it!
To learn more:
- Video comparing the June and December solstices on my YouTube channel
- Wikipedia article about the astronomical solstice