A Great "Get-together"

 

One of the rare events in the sky is a conjunction of the two largest planets in our solar system.

I logged into Slooh.com on December 21 to watch their live presentation as this conjunction was in progress. There was also a link to the International Astronomical Center in Abu Dhabi, U.A.E.  The image below originated there; it was shown during the presentation, Saturn at the upper left, Jupiter lower right. 

One day later, the Simon Fraser University's Trottier Observatory did the same thing through its telescope on line, with assistance by the RASC. I also watched that well done presentation via YouTube.

Jupiter/Saturn conjunction (International Astronomical Center)

This conjunction was the result of a particular positioning of Jupiter, Saturn, and Earth in their respective orbits. At the time pictured, the visual separation in the sky of Jupiter and Saturn was about six arc minutes, which is about one fifth of the apparent diameter of our Moon as we see it from Earth. That essentially "united" the two planets into one brighter "star" when looking with our unaided eyes. In reality, Saturn is about 700 million kilometres "behind" Jupiter from Earth's point of view. For perspective, Jupiter is approximately five times Earth's distance from the Sun, Saturn almost twice as far.

The large planets in our solar system orbit the Sun in approximately the same plane; Earth's orbital plane is taken as the reference. As a result, the sun 's annual apparent motion across the sky from Earth appears to be the same from year to year with very small changes over time. This path is called the Ecliptic. The larger planets have orbital planes which are close to the ecliptic, but deviate from it to varying degrees. From our Earth-bound point of view, therefore, for them to appear very close together, such as the Jupiter-Saturn conjunction, happens only now and then. Jupiter can even cover (occult) Saturn, but that is a very rare occurrence. It would require that the centres of Earth, Jupiter, and Saturn be exactly on one specific line. The latest Jupiter-Saturn conjunction came very close to that possibility.

The two planets move quite slowly. Jupiter takes about 3 hours for a distance equal to its own diameter, Saturn is even slower. Both move in the same direction. That means the they will be visible in a pair of binoculars at the same time for a number of days. Standard binoculars have fields of view in the order of 5 to 7 degrees. On January 1, 2021, Saturn and Jupiter are about 2 degrees apart, easily within the same  binocular field of view. Unfortunately they are positioned so close to the sun at this time that they will set closer to sunset every day, so following both planets is going to get more difficult. For this purpose, use your binoculars only after the sun sets. Never look at the sun directly through binoculars, or even with your unprotected eyes only; permanent eye damage may be the result!

Covid-19 is forcing us to keep separate for the time being, it was a good thing to see at least one "heavenly" get-together.