Calendar winter begins on December 1, astronomical winter – on December 22. But it feels as if winter comes into its own in the first month of the year – it is usually in January that the weather is coldest. Atmospheric scientist Deanna Sino explained why this happens from a scientific point of view.
As the Earth revolves around the Sun, it rotates on its axis – imagine a straight line passing through the Earth from the North Pole to the South Pole. During the 24 hours it takes the Earth to make one rotation on its axis, each point on its surface faces the Sun part of the time and is turned away from it part of the time. This is what causes the daily changes in sunlight and temperature.
There are two more important factors: first, the Earth, though not perfectly, is nonetheless round. Second, its axis is tilted by about 23.5 degrees relative to its path around the Sun. As a result, light falls on the northern and southern poles at an angle.
When one of the poles is tilted more toward the Sun than the other, that half of the planet receives more sunlight, and summer comes to that hemisphere. When that pole tilts away from the Sun, winter comes.
At the equator, which constantly receives direct sunlight, the length of day and the temperature hardly change throughout the entire year.
Why does it often grow colder in January, despite the fact that daylight is already lengthening?
The Earth's surface constantly absorbs the Sun's energy and stores it in the form of heat. And it also radiates heat back into space.
Why plastic windows sweat in frost and how to deal with it The farther north you live, the more time it takes for the amount and intensity of daylight to begin to increase significantly after the solstice, since your location is farther from the Sun. But even the areas that receive little sunlight continue to radiate heat into space. As long as they receive less sunlight than the heat they radiate, they will keep growing colder. This especially applies to land, which loses heat far more easily and quickly than water.
By the way, the Southern Hemisphere has much less land and more water than the Northern. It is precisely thanks to the influence of the oceans that the land in the Southern Hemisphere tends to have fewer temperature extremes than in the north.
