December Solstice in New York, New York, USA is on Monday, December 21, 2020 at 5:02 am EST
the staff of the Ridgewood blog
Ridgewood NJ, Astronomically speaking, this week heralds the end of fall and the beginning of winter in the northern hemisphere. Though meteorologists like to define the seasons differently—with winter beginning on December 1 each year—astronomers say that winter begins on the date of the solstice.
A solstice is an event that occurs when the Sun appears to reach its most northerly or southerly excursion relative to the celestial equator on the celestial sphere. Two solstices occur annually, around June 21 and December 21. In many countries, the seasons of the year are determined by reference to the solstices and the equinoxes.
This year, the solstice happens to converge with a “great conjunction” that some have christened as an early “Christmas star” because of its occurrence near the holiday.
According to NASA , Jupiter and Saturn have been traveling across the sky together all year, but this month, get ready for them to really put on a show. Over the first three weeks of December, watch each evening as the two planets get closer in the sky than they’ve appeared in two decades. Look for them low in the southwest in the hour after sunset. And on December 21st, the two giant planets will appear just a tenth of a degree apart – that’s about the thickness of a dime held at arm’s length! This means the two planets and their moons will be visible in the same field of view through binoculars or a small telescope. In fact, Saturn will appear as close to Jupiter as some of Jupiter’s moons.
This event is called a “great conjunction.” These occur every 20 years this century as the orbits of Earth, Jupiter, and Saturn periodically align making these two outer planets appear close together in our nighttime sky. Even so, this is the “greatest” great conjunction between Jupiter and Saturn for the next 60 years, with the two planets not appearing this close in the sky until 2080.
When these two planets converge on Dec. 21 they will be the closest they’ve been to one another in the night sky since 1623, according to Joe Rao, instructor at the Hayden Planetarium in New York. But that conjunction wasn’t visible to skywatchers on much of the Earth because of its location in the night sky. The last time the event was visible from most of the Earth was in 1226, according to Virginia Tech astronomer Nahum Arav.
“This rare event is special because of how bright the planets will be and how close they get to each other in the sky,” Arav said in a statement.
The 21st is also the date of the December solstice, which is the winter solstice in the Northern Hemisphere and the summer solstice in the Southern Hemisphere. On the December solstice, the Sun reaches its southernmost position in the sky, no matter where on Earth you happen to be.
It’s possible that their meeting on Dec. 21 might produce a “winter star” as their lights coalesce and appear like a single point of reflected light with the naked eye.
