BOSTON (CBS) – In a year when “social distancing” has become the norm, how ironic that we’re going to celebrate something called the “Great Conjunction”. While we Earthlings stay a safe distance from each other, Saturn and Jupiter are doing just the opposite! On December 21st, these two giant planets will appear closer to the sky than ever before in the last 400 years! Yes, you read that right: the last time Saturn and Jupiter were this close, Galileo was watching!
This year’s planetary show, commonly referred to as the “Christmas Star”, promises to be out of this world. The next time they approached around 1 p.m. On the 21st, the two planets appear only 0.1 degrees apart. By the time we can examine them that night, they will already have spread apart, although they still seem almost to be touching.
This begs the question of whether they will ever cover up exactly. This is really a rare opportunity, the last occultation was in 6857 BC. And the next not until 7541 AD.
Of course, the planets are not really close to each other at all; in fact, they are hundreds of millions of miles apart. Only from the point of view of the earth do they seem almost to be touching. Jupiter, which is closer to the earth and the sun than Saturn, is moving at a much faster orbital speed than Saturn. And from our place here on earth, we are essentially watching Jupiter catch up with Saturn and pass before it. Given the tilt of the solar system, we observe at an angle, which is why it is so rare that they actually go directly over one another.
What’s the best way to see this once in a lifetime event?
First and foremost, you need to have an unobstructed view of the southwest sky, away from as much natural light as possible. (Even though the planets are so bright, you can see with the naked eye even in the city).
You need a good view of the horizon as the planets are only about 14 degrees above the ground.
Start your search around 45 minutes after sunset (around 5 p.m.). You only have a few hours because they set around 7 p.m.
So what is what?
In the nights before Saturn 21st, Jupiter will head towards Jupiter from the top left and will get closer and closer every night. Jupiter will be the brighter star of the two and appear on Saturn’s lower right.
On December 21st, Jupiter will overtake Saturn and essentially swap places in the night sky.
If you have binoculars or a telescope, you get an added bonus! Many of the moons of Jupiter and Saturn will also be visible during conjunction.
If you miss it, you have to wait a bit to see something so breathtaking. On November 4th, 2040, they will appear about 1.2 degrees apart … meh, ok. They only approach this again in the 2400s.
Happy Sky Watching!
Follow Terry on Twitter @TerryWBZ