Triple Act, Part One

Yes, I was away during the best planetary conjunction of the year.

ho150630evVenJup

The moment of the planets’ closest approach to each other (appulse) fell in July 1 at about 3:30 by Universal Time.  The dots for them have to be exaggerated in size so that you can see them: Venus and Jupiter were 33 and 32 seconds (1/3600ths of a degree) wide, and the gap between them was about 1200 seconds. The arrows through the moving bodies show their movement (against the starry background) from 2 days before to 2 days after.

I came home the day before yesterday, to find that “Pirate” Jack Gambino (burly and exuberant hombre living in upstate New York, former head gardener for New York City – I may have some of that inexactly) filled in for me by posting comments here; I hope you saw them. As he brightly said, the planets were “a whisper-thin 1/3rd of a degree apart” and you could “hide the pair behind your little pinky finger outstretched at arm’s length.”

Venus passes Jupiter every 13 months on average (because that is Jupiter’s synodic period, the time it takes us to overtake it). The conjunctions can be as little as 10 or as much as 15 months apart.

But this year is one of those in which the Venus-Jupiter conjunction is triple. On July 1 Venus moved forward past Jupiter; but, rounding its orbit which is so much nearer to us than Jupiter’s, it will halt and on July 31, also in the evening sky, fall back past Jupiter, then past the Sun; and, in the morning sky, it will overtake Jupiter again on October 26.

sfCjVenJup

The last such triple conjunction was in 1991 (June 17, Aug. 23, Oct. 17). That was three of Venus’s 8-year cycles ago, but this is not a rule: the next triple conjunction will be in 2036. It can happen only around a time when Venus passes in front of the Sun near when Jupiter passes behind it (this year these dates are Aug. 15 and Aug. 26).

The first conjunction of the year’s three is the close one: Venus only 0.336 degree south of Jupiter. (On July 31 it will be 5.4 degrees south, on Oct. 26 1 degree.) This is not the closest it can be: on 2000 May 17 the gap was only 1 minute (1/60 degree). Nor is it the closest planetary conjunction of this year: that was Venus-Uranus (0.09 degree) on March 4. But any time these two most brilliant of planets huddle as closely as they do now, they make a double star like no other in the sky.

Jean Meeus points out yet more about the patterns of Venus-Jupiter conjunctions, especially the triple ones, in his Mathematical Astronomy Morsels II, pages 258-260, and IV, 252-261.

I did watch Venus approaching Jupiter, from shipboard across the Bay of Biscay, and then from Fisterra in Galicia on June 29.

FisterraVenusNJupiter-150629

The Sun had set, three-quarters of an hour ago, exactly where the sea meets the headland on the right, about which I shall have more to say, because it is the End of the Earth.

 

4 thoughts on “Triple Act, Part One”

  1. Wow, Eric! What a great gallery of pix you have! I really ought to hook you up with my friend in Utah who’s into astrophotography as well, possibly by forwarding this edition of Guy’s blog to him. Your pix of the aero-space museum reminds me of a campaign I’d like to start to save Hubble telescope. Rather than allow it to return to earth in some fiery crash somewhere, hopefully in an ocean, why shouldn’t we send up a shuttle to bring it back safely and put it on display at the Smithsonian or something? But I digress. More at some other time.
    Guy, I LOVE you’re diagrams depicting the planetary motions around the sun. I try to describe it all by telling folks to hold their hands and arms length with index fingers aimed at each other, then trying to circle in towards your body, one hand clockwise and the other counter-clockwise. Wheels in constant motion.

  2. I enjoyed reading Jack’s comments while you were away, Guy, as well as your own commentary about this wonderful planetary conjunction. Unfortunately, here in central Virginia, the weather has been horrible, so we have only had a few evenings during which you could even see Venus at all, and the main event on the 30th of June was clouded out. I did manage to get a couple of decent shots on June 29, which are at https://www.flickr.com/photos/starvergnuegen/ Yesterday, I was able to see Venus and Jupiter during the daytime with 10×50 binoculars; seeing them during daylight really highlights the huge difference in surface brightness between the two!

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