# The Dark Crystal **URL:** \ **Category:** Factual Questions\ **Created:** [June 12, 2009, 8:30am UTC](https://boards.straightdope.com/t/the-dark-crystal/499539 "2009-06-12T08:30:53Z")\ **Posts on this page:** 6\ **Page:** 1
**Author:** ![rust1729](https://avatars.discourse-cdn.com/v4/letter/r/7c8e57/32.png) [@rust1729](https://boards.straightdope.com/u/rust1729)\ **Post date:** [June 12, 2009, 8:30am UTC](https://boards.straightdope.com/t/the-dark-crystal/499539/1 "2009-06-12T08:30:53Z")
In the movie there is an alignment that only happens every 1,000 years between their 3 suns and they call it the great conjunction. Ever since I saw the movie I have wondered, on what day will all of our planets align? The rest of the planets have a slightly tilted orbit in comparison to ours. However, inevitably they will all lie on 1 plane at some point; when will that occur, including the planets not visible to the naked eye? I’d like to find out without coding an orrery program, but will do it if necessary. ---
**Author:** ![Sage\_Rat](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/sage_rat/32/399_2.png) [@Sage\_Rat](https://boards.straightdope.com/u/Sage_Rat)\ **Post date:** [June 12, 2009, 8:40am UTC](https://boards.straightdope.com/t/the-dark-crystal/499539/2 "2009-06-12T08:40:48Z")
Do you want them to be on the same plane or on the same plane + lined up with one another? The second is significantly more difficult. ---
**Author:** ![dtilque](https://avatars.discourse-cdn.com/v4/letter/d/d6d6ee/32.png) [@dtilque](https://boards.straightdope.com/u/dtilque)\ **Post date:** [June 12, 2009, 10:09am UTC](https://boards.straightdope.com/t/the-dark-crystal/499539/3 "2009-06-12T10:09:30Z")
I think what the OP means by the same plane is a plane perpendicular to the ecliptic. In other words, lined up as well as they can given the different inclinations of their orbits. There was a silly scare back in the 70s/80s about how the planets would all lineup and cause something bad to happen. Earthquakes or something. Total silliness, but someone wrote a book called the [Jupiter Effect](http://en.wikipedia.org/wiki/Jupiter_Effect) promulgating it. The thing is, in the Jupiter Effect scenario, the planets are not lined up. They were more-or-less in the same quadrant. Or a bit less lined up than the players in a baseball game. This kind of line up happens every so often (several times per century) and is not especially remarkable. Line ups with them in a narrower angle, say less than 45 degrees, are much rarer, perhaps happening every 10,000 years or so. ---
**Author:** ![beowulff](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/beowulff/32/542_2.png) [@beowulff](https://boards.straightdope.com/u/beowulff)\ **Post date:** [June 12, 2009, 12:44pm UTC](https://boards.straightdope.com/t/the-dark-crystal/499539/4 "2009-06-12T12:44:42Z")
“When the Moon is in the Seventh House…” ---
**Author:** ![WarmNPrickly](https://avatars.discourse-cdn.com/v4/letter/w/d78d45/32.png) [@WarmNPrickly](https://boards.straightdope.com/u/WarmNPrickly)\ **Post date:** [June 12, 2009, 1:01pm UTC](https://boards.straightdope.com/t/the-dark-crystal/499539/5 "2009-06-12T13:01:03Z")
If you define the plane infinitely, it will never happen, so you will have to define an angle that’s allowed. I remember that Jupiter effect thing. It was pretty silly. ---
**Author:** ![OttoDaFe](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ottodafe/32/356_2.png) [@OttoDaFe](https://boards.straightdope.com/u/OttoDaFe)\ **Post date:** [June 12, 2009, 1:57pm UTC](https://boards.straightdope.com/t/the-dark-crystal/499539/6 "2009-06-12T13:57:29Z")
Well, the [Harmonic Convergence](http://en.wikipedia.org/wiki/Harmonic_Convergence) has come and gone, and the universe appears still to be here (without the predicted love and unity). I seem to recall an entry in Dave Barry’s annual recap in which he described the True Believers celebrating the event by chewing on the ends of their straitjacket straps.