Shirin Ali wrote at thehill.com yesterday:
“The month of December brings cold weather for many and lots of holiday spirit, but for astronomers it marks the beginning of the winter season with the winter solstice, when the sun travels the shortest distance through the sky.
The winter solstice is the precise moment when the Earth’s North Pole points directly away from the sun, at about 23.4 degrees. That’s projected to happen tomorrow at 4:48 p.m. EST, which means Tuesday, Dec. 21 it will be the shortest day of 2021 in the Northern Hemisphere, adding up to just 8 hours and 46 minutes of daylight, according to Space.com.
The winter solstice marks the beginning of the astronomical winter which runs from December until the following year’s spring equinox. In 2022, the spring equinox is expected to take place on March 20.
Just as the Northern Hemisphere experiences winter, the Southern Hemisphere is entering summer.
After Tuesday, days in the Northern Hemisphere will get progressively longer as Earth journeys back around the sun, an astronomical event that astronomers celebrate because it marks Earth’s tilt on its axis and its motion in orbit around the sun.
Earth’s orbit isn’t completely upright because its axis is always tilted at 23.5 degrees, which is what gives our planet seasons. For example, during the June solstice the North Pole is positioned more directly towards the sun while the South Pole is directly away from the sun. That results in the northern half of the equator experiencing longer 12-hour days that are warmer and the southern half of the equator getting shorter than 12-hour days.
Just as the winter solstice gets underway, another astronomical event will occur shortly after. The Ursid meteor shower will likely peak on the morning of Dec. 22, which means sky-gazers may see a flurry of meteors after midnight and possibly into sunrise.”