In astronomy a conjunction is when two or more planets come very close to each other in the sky because their orbits line up with the Earth’s orbit. On December 21, we will be treated with not only a conjunction of two planets, but a great conjunction. Just after the sun sets the planets Jupiter and Saturn will appear so close to each other they will appear to the human eye to be one bright planet.
This is an illusion as they will be 400 million miles apart.
Jupiter orbits the Sun about ever 12 years while Saturn orbits the Sun about every 30 years, so they appear close together from Earth about every 20 years. The last time was on May 28,2000.
But this year the conjunction is ever rarer. This year the distance they will appear from each other is so close, that we would have to go back to March 4, 1226 to get a closer observable alignment. That’s 800 years ago. Usually they are 2-4 degrees apart.
The planets began their approach this summer. From Utah Jupiter and Saturn are easily seen in the southwest sky after sunsets, the next few weeks. But mark your calendar for December 21 when they will be the closest, only 0.1 degree apart. A small telescope will give great views of both planets and their moons in the same field of view, but a good pair of binoculars will give a good view as well.
The winter solstice is also on December 21. After that date the two planets will start to move a part from each other. Watching the two planets move toward each other then away will be a memorable event.
If you miss it this year, this same event will take place in 60 years, on March 15, 2080.
