In the United States and the rest of the northern hemisphere, the first day of the winter season is the day of the year when the Sun is farthest south (on December 21

In the United States and other parts of the northern hemisphere, the first day of winter is the southernmost point of the sun (December 21 or 22). This day is called the winter solstice.

The declination of the sun during the winter solstice is called the Capricorn regression line (-23 ° 27 '). In the Southern Hemisphere, the winter solstice and the summer solstice are exchanged so that the winter solstice becomes the northernmost tip of the sun.

A common misunderstanding is that the earth is far from the sun in the winter than in the summer. In fact, the earth is closest to the sun in December, this is the winter of the northern hemisphere.

When the earth goes round the sun, the north-south position of the sun changes throughout the year as the direction of the tilt axis of the earth changes. The date of the maximum inclination of the Earth's equator corresponds to summer solstice and winter solstice, and spring equinox and autumn equinox date.

The reason for these changes is related to the Earth's annual sun travel. During the year, the Earth's Arctic is pointing away from the sun. This is the reason for this season. When the Arctic is pointing to the sun, the ray of sun more directly hits the northern half of the world. It's warm, we have summer

The winter solstice is the shortest day of the year. The length of time between sunrise and sunset of this day is the smallest of that year. In America, today's sunlight has only about nine and a half hours.

At northern latitude 40 degrees, the earliest sunset of that year occurs around December 8, the latest sunrise will occur around January. The lowest day of the day (the first day of winter) is December 21st. Why are not all these dates the same? For detailed explanation, please see "Dark Winter Day" on the US Naval Observatory website.

Ready - Ready.gov is a National Public Service Advertising (PSA) campaign aimed at educating and giving power to Americans to prepare for emergencies including natural disasters and human-induced disasters. The purpose of this event is to involve the general public and ultimately improve the basic preparation level nationwide.

Four seasons and the earth 's orbit - through the naval oceanography portal, the US Navy Observatory provides astronomical information on the relationship between the orbit of the earth around the sun and its seasonal change.

The seasonal astronomical definition is related to a specific point of the earth around the sun. Summer and winter solstice, the longest and shortest day of year, the axis of the earth occurs at the nearest or furthest point from the sun. According to the National Oceanic and Atmospheric Administration, the summer solstice of the Northern Hemisphere occurred around the same June 21 as the Winter Solstice of the Southern Hemisphere. The summer solstice in the south is December 21 and the winter solstice in the north. In both hemispheres the summer solstice shows the first day of the astronomical summer and the winter solstice is considered the first day of the astronomical winter.

Today we are a modern day calendar, marking this day as the winter solstice of December 21. Around the winter solstice, the northern hemisphere experienced the longest night in a year; it took about three days to observe the sun again northward along the horizon, and witnessed the beginning of the day. In other words, in this dark moment, we are also waiting for the regeneration of light. The last day of Saturnalia has become a festival filled with bright and full candles symbolizing the pursuit of trust and knowledge. In the second century, at the end of Saturn, the Sun festival had its own name: "Dies Natalis Solis Invicti"