This event has not happened for 800 years. As Christmas approaches, sky gazers will be treated to a celestial wonder that hasn’t been seen so clearly since 1226 — a “Christmas star.”
Information via solarsystem.nasa.gov
12/07/2020 – 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.
Credit:NASA/JPL-Caltech
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.
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.
In the Northern hemisphere, the Sun travels its lowest, shortest path across the sky on that day. Thus, in the north, the winter solstice brings the shortest day of the year, in terms of hours of sunlight.
Now the Sun’s changing height in the sky throughout the year is caused by Earth’s tilt as it orbits our local star. The tilt causes the amount of sunlight each hemisphere receives to go up and down in the annual cycle of the seasons.
Credit:NASA/JPL-Caltech
