Bright lights in the West; Get ready for the Big One!

I'm coming out of my work-induced blog-semi-retirement to let you know of some very important celestial events coming up.  If you've been looking to the West shortly after sunset for the last month, you've been seeing Jupiter gradually getting lower in the dusky sky.  If you have a low enough western horizon, you may have noticed Venus slowly approaching the giant planet.  This weekend, the two will be closest together in the sky, called "Conjunction."  Here is a sample view of what you might see if you have clear skies:

Screenshot from Stellarium 0.14.3

The time and position of the planets is set for Boulder, CO.  If you live in the northern hemisphere, you'll likely see something similar to this about 30 minutes after sunset.

Once it gets late enough that these two of the brightest night sky objects begin to pass over the horizon, take a moment to notice a third planet nearby.  Just a little above and to the left of the pair sits the Ringed planet, Saturn.  It may be a little more difficult to identify it, because it is nearly twice as far away as Jupiter and so is somewhat fainter.  But, in just two more weeks, it'll become much easier.  Because (with apologies to Sam Cooke) Venus sees Jupiter comin' and she'll just pass him by.  Venus continues her trek Eastward through the sky, and pays Saturn a visit on 10 December.  Here is a view of how that might look:

Screenshot from Stellarium 0.14.3

The time of day is about the same; but the sky is a little darker, because sunset is about five minutes earlier on 10 December (in fact, the earliest sunset of the year is usually very close to this date, for northern hemisphere mid-latitudes; maybe we'll talk about that in a future blog).  This image approximates the view about 45 minutes after sunset.

Now, you might think it is unusual to have two close conjunctions just a few weeks apart, and you'd be right.  And, in this case, it is a hint to an even more spectacular conjunction yet to come!

You see, Jupiter moves through the sky a little more quickly than Saturn because it is closer to the Sun, and so has a shorter year.  In fact, to the ancient Greeks and Romans, Saturn was the slowest planet in the sky, taking over 30 years to return to the same spot; so they named it after their god Cronus, a god of time (among other things).

Well, roughly every 19.5 years, Jupiter and Saturn, the two largest planets in our Solar System, team up for what is sometimes called the "Great Conjunction." We're due for the next one in about a year.  And, mirabile visu, what a conjunction this promises to be!  Next year, if you were to look West on the Northern Hemisphere Winter Solstice at about half an hour after sunset, you'd see this:

Screenshot from Stellarium 0.14.3

Where's the conjunction, you say?  You see only one object?  Let's pull out our virtual telescope:

Screenshot from Stellarium 0.14.3

If you time it right, you will capture a view of Saturn and Jupiter so close together that it would appear as though Jupiter could be one of Saturn's moons!  In fact, some of the fainter objects in this view are moons of Saturn: Iapetus, Rhea, and Titan.  Saturn takes a few days to "pass though" the Jupiter system (I told you Saturn moved slowly through the sky).  Well, technically it is Jupiter that moves through the Saturn system as viewed in the sky, since it is moving faster.  So, you'll have a few days to see this spectacular conjunction. 

As an aside, these "Grand Conjunctions" have been viewed by Astrologers for millennia as harbingers of great change.  In fact, another Grand Conjunction about two thousand years ago was particularly noteworthy.  You might recall that about five years ago, Jupiter and Venus were aligned in such a way with the Earth that they performed an intricate and rare dance in the sky that resulted in three close conjunctions over the span of about a year.  This (with limited originality) is called a "triple conjunction."  Well, a little more than two thousand years ago, the Great Conjunction was similarly also a triple conjunction.  Over the course of about six months, Jupiter and Saturn came together three separate times in the constellation Pisces.  It has been suggested that this event, of which Astrologers of the era would have definitely taken notice, could be the "Star of Bethlehem," that the Magi in the Christmas narrative interpreted as a sign that a great leader had been born.

So, here is your one Jovian Synodic Period (13 months) Advance Warning: start making plans to be in a dark spot with climatologically clear evenings for Winter Solstice, 2020.  Don't miss your chance to see the Conjunction of the Century!