Mnemonic having written:
<I don't think it's likely that the inhumu go back and forth as often as people have previously speculated. In both books I believe, Horn says that even when the two planets are at conjunction, the trip between is dangerous and many inhumu do not survive (forgive me for not having and exact reference.)>
Here are some numbers I hope will help bring things a little more into perspective about the trip from Green to Blue. They prove nothing other than the arduous nature of the trip for creatures more familiar to us.
Green and Blue, at their closest point, are 35,000 leagues apart; this has been determined by Gagliardo, the Soldese astronomer.
At 3 miles per league (LEXICON URTHUS), this amounts to 105,000 miles--over four times the circumference around the Earth at the equator.
For a flock of geese to fly this distance, it would have to fly, at 50 mph (its normal migratory speed) twenty-four hours a day, a total of 87 days, or nearly three months.
Of course, maybe the inhumi can fly faster than 50mph, although I'm still not sure how they propel themselves over that 105,000 miles of void. (I'll spare you my theory about short digestive tracts and le Petomaine-type locomotion.)
Robert Borski
*This is WHORL, for discussion of Gene Wolfe's Book of the Long Sun.