The 'great conjunction' of Jupiter and Saturn: what to expect

Keeping an eye on the forecast for December's planet alignment
Posted at 4:18 PM, Dec 15, 2020
and last updated 2020-12-15 18:32:15-05

MISSOULA — Mark your calendars.

Another exciting celestial event is occurring December 21st!

It may have been hard to tell these last few days with clouds and snow taking hold of our forecast, but Jupiter and Saturn have been inching closer and closer on our horizon since September.

These two planets continue their trajectory to closely align and will appear as a single “star” on our horizon December 21st.

They will still be far apart in their actual orbit, but from Earth’s view, it will appear as they are one in the sky.

A conjunction is when two objects look very close to the naked eye in our sky, but the conjunction of Jupiter and Saturn is called a great conjunction and only happens once every 20 years.

So, if it happens every 20 years why is this great conjunction so special?

This will be the closest great conjunction since July 16, 1623 as these planets will only be separated by 0.1 degrees from Earth's vantage point.

Therefore, they appear as a single “star.”

So when can you see it?

Well depending on the forecast, which looks mostly cloudy, snowy, and rainy right now, in the off chance there is some clear sky over Western Montana on December 21st, the best time to view will be right after sunset on the southwest horizon.

The next time a great conjunction will occur will be November 2, 2040 and April 7, 2060, but even then the separation of the two planets will be 1.1 degrees which is ELEVEN TIMES farther apart than it will appear this year.

Fun fact: other great conjunctions with less than 0.2 degrees of separation have occurred: 1623, 1683, 2020 and will occur again in 2080, 2417, 2477.

So after December 21, 2020, it will be another 60 years before these two planets align this closely.