The longest days are accompanied by the winter solstice
When we say that the longest day of the year always comes at the winter solstice, the day here does not refer to a certain period of day, but to the interval from noon to the next noon of the sun. In December, a day, the Earth's rotation relative to the midday sun, is about 0.5 minutes longer than the usual 24 hours.
This year, the winter solstice arrives at 10:02 a.m. INTERNATIONAL STANDARD on December 21. That is, 4:02 a.m. on the 21st in the Central Time Zone of North America. For those of us who live in the Northern Hemisphere, the winter solstice takes us into the shortest days and longest nights of the year.
However, if we consider the length of a day from another angle, the longest day of the year in the world will appear in December of each year.
Remember that the clocks on our walls cannot accurately measure the true duration of solar days. If you want to measure the time from noon one sun to noon of the next, you need a sundial. The sundial will tell you the exact local time of the sun at noon—when the sun reaches the highest point of the day.
In the close-up photo above, the shape of the 8 printed on the globe is an Earth orthographic projector. The Earth orthographic projector can simulate the tilt of the Sun, that is, the angular distance between the Sun and the celestial equator, and the difference (in minutes) between the time measured by the clock and the time measured by the Sun.
So now in December, that means that one rotation of the Earth around the Sun — what we call solar days — is about 1/2 minute longer than the Earth's average of 24 hours a day.
The time from noon one sun to noon on the next around the winter solstice is always longer than 24 hours, and around the vernal equinox it is shorter than 24 hours.
The days are now the longest for the entire planet because we are closer to the sun in December than we were in June. Earth's perihelion — the closest point to the Sun — always appears in early January. When we get closer to the Sun, our planet will move a little faster in orbit than the average. This means that our planet travels a little farther through space than the average per day. This causes the Earth to rotate a little more in its orbit so that the Sun returns to its midday position, so the Solar Day will be a little longer.
Half a minute doesn't sound like much, but it adds up to a noticeable difference. For example, in the two weeks leading up to the winter solstice in December, the noon time is about seven minutes earlier than the December winter solstice day. Two weeks after December's winter solstice, noon is about seven minutes later than on December's winter solstice. Since the clock and the sun are most out of sync at this time, some unusual phenomena cause people to be most confused at this time of year.
Check out the sunrise and sunset calendar website for local solar noon time, or check it out through the Solar noon box.
In the Northern Hemisphere, the earliest sunset of the year is before the winter solstice in December, while the latest sunrise of the year is after the winter solstice in December.
In the Southern Hemisphere, the earliest sunrise of the year precedes the summer solstice in December, while the latest sunset of the year is after the december solstice.
Although solstice days are shortest/longest, the earliest sunsets/sunrises are always before solstice and the latest sunrises/sunsets are always after solstice.
We are closest to the sun in early January, which also means that the winter in the Northern Hemisphere (summer in the Southern Hemisphere) is the shortest of the four seasons. At the same time, it is also a season with very long days.
Sundial outside the Adler Planetarium in Chicago, Illinois. Sundials allow you to measure the time from noon one sun to noon the next. Image credit: Ben + Sam.
Summary: From noon on one day to noon on the next day, December has the longest daytime and longest day-night cycle for the entire planet.
Related knowledge
The winter solstice, cold solstice, or cold solstice, also known as midwinter, occurs when the Earth's poles are tilted the most away from the Sun. It occurs twice a year, once in each hemisphere (northern hemisphere and southern hemisphere). For the Northern Hemisphere, the winter solstice is the shortest day of the year and the longest night of the year, when the sun is at the lowest point of its daily altitude in the sky. In the Arctic, around the winter solstice is a continuous polar night. The opposite is the summer solstice. There is both the Tropic of Cancer and the Tropic of Cancer on Earth, depending on the hemispheric winter solstice, where the sun reaches its lowest point perpendicular to the horizon.
The winter solstice occurs during the winter months of the Northern Hemisphere. In the Northern Hemisphere, this is December to Sunday (usually December 21 or 22), and in the Southern Hemisphere, this is June to Sunday (usually June 20 or 21). Although the winter solstice itself only lasts for a certain period of time, the term sometimes refers to the day on which the winter solstice occurs. Other names include "Midwinter", "Cold Winter", or "Shortest Day". In many temperate regions, the winter solstice is considered the middle of winter, but today in some countries and calendars, it is considered the beginning of winter. Meteorologically, winter begins about three weeks before the winter solstice.
Since ancient times, the winter solstice has been seen in many cultures as a sign of important festivals and rituals of the year. It symbolizes the death and rebirth of the sun. The seasonal significance of the winter solstice lies in the gradual lengthening of the night and the gradual shortening of the day.
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FY：Astronomical volunteer team
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