I'm working on a kids book and need an astronomical configuration that would occur about every 100 years and could be represented on a planetarium ceiling. The more colorful the better. Suggestions or links?

Transits of Venus occur in pairs (sorta) a little more than one hundred years apart. I dunno how colorful that would be on a planetarium ceiling--but what astronomical event is all that colorful when projected scaled size onto a planetarium?

And the next Venus transit is in June of 2012. From that website: "Historically, global expeditions timed transits of Venus to quantify the size of the solar system".

I'll look into it.

Comet Halley swings by every 76 years or so.

Fred

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Conjunctions of Mars, Jupiter, and Saturn all at once happen about that often.

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One which happens a little bit more often: Mars closer approach to Earth. Normally, the Earth catches up to Mars about every 2.2 years, and Mars increases in magnitude until it is somewhere between magnitude -1 and -1.5 or so. That's impressive, but Mars has a more elliptical orbit, so that it is much closer to the Sun (and Earth's orbit) once per each of its 687 day (1.9 years) period. The Earth only catches up to Mars during its close approach every fifteen or seventeen years or so, at which time Mars becomes nearly mag. -3, and very bright.

You'll be getting an email about it soon.

You get the four giant planets on one side of the sun--the alignment that Voyager took advantage of--once every 170 years or so.

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Is there an astronomical term for the Conjunction of Mars, Jupiter, and Saturn?

triple conjunction

Some upcoming conjunctions are detailed at:
http://en.wikipedia.org/wiki/Astronomical_conjunction

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Triple conjunction of the Superior Planets. Personally, I think of this as an astrological term more than astronomical, but it applies to both. It is a conjunction of the three planets whose orbits were outside the orbit of the Sun (using the pre-Copernican view).

Astrologers believed that such conjuctions had powerful effects that take about three years to come to fruition. There was such a conjunction in 1345 that they blamed the Great Plague (1348-1351) on. In the 1520s there was such a conjunction in Aquarius, and astrologers predicted heavy flooding (Noah-like).

Please note that such a conjunction normally has several episodes of two planets being very close together over the course of a few months. It doesn't involve three planets all in a spot the size of the moon at one time. They are just all in the same zodiacal constellation as each other.

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