Saturn hesitates before the Great Conjunction

On Tuesday, September 29, Saturn will become stationary – a sort of prelude to its Great Conjunction with Jupiter in December.  We’ll have to say and show a lot about that when it comes.  Here’s a foretaste.

See the end note about enlarging illustrations.

In this spatial view, constellation boundaries are drawn on an imaginary sphere with radius 10 astronomical units (Sun-Earth distances), just beyond Saturn’s 9 a.u.  The dashed line is the vernal equinox direction, in Pisces.

Jupiter overtakes Saturn at intervals of about 20 years  Each next conjunction is about 2/3 of the way on onward around the circle.

The lines are from Jupiter to Saturn at the dates of conjunction.  They could be from Earth-to-Jupiter-to-Saturn, because they are really sightlines from Earth to the planets.

To try to make the rhythm clear, I show an early group of three (1940, 1961, 1981) in orange, a middle group (2000, 2020, 2040) in yellow, a later group (2060, 2080, 2100) in green.

Two of the conjunctions of the twentieth-century group are of the triple kind: Jupiter appears to pass Saturn, retreat, and overtake again.

Thicker gray lines are at the true centers of the events: the heliocentric conjunctions.  For 2020, this will be November 2.  The lines could be extended back to the Sun (missing the Earth): at those moments, Jupiter and Saturn are at the same direction (longitude) as seen from the Sun.  The conjunctions as seen from Earth are displaced irregularly around these heliocentric conjunctions, because of where Earth happens to be in its faster little orbit.

Well, more on that as the Great Conjunction approaches.  Here is Tuesday evening’s sky scene.

The ecliptic is a busy highway.  Saturn, having been at opposition on July 20, is falling back ever nearer to Jupiter.  Jupiter and Saturn will be at east quadrature – 90° from the Sun – on October 11 and 18.  Our Earth is traveling away from the antapex of its motion, also about 90° from the Sun.  Arrows through the moving bodies, including the Sun, show their motion over 5 days.

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ILLUSTRATIONS in these posts are made with precision but have to be inserted in another format.  You may be able to enlarge them on your monitor.  One way: right-click, and choose “View image”, then enlarge.  Or choose “Copy image”, then put it on your desktop, then open it.  On an iPad or phone, use the finger gesture that enlarges (spreading with two fingers, or tapping and dragging with three fingers).  Other methods have been suggested, such as dragging the image to the desktop and opening it in other ways.

Sometimes I make improvements or corrections to a post after positing it.  If you click on the title, rather than on ‘Read more’, I think you are sure to see the latest version.

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