Can moons orbit moons? — the poem

Can moons orbit moons? wondered Juna and I.
Some planets have moons, you know, up in the sky
But none of those moons has its own moon around it.
When Juna’s son learned this he just was astounded!

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A cigar from another star

In Rendezvous with Rama (by Arthur C. Clarke), a mysterious object is discovered passing through the Solar System.  The object has a strange shape — it’s a giant cylinder.  It was discovered by the Spaceguard survey, designed to find objects that might impact Earth (so-called near-Earth objects).  Spoiler alert: the cylinder is a spaceship sent…