Learn French: À peine l'homme voit-il la comète qu'elle disparaît. - Barely does the man see the comet when it disappears.

This is a perfect example of complex inversion. When a sentence begins with certain adverbs like À peine (barely/hardly), formal French requires subject-verb inversion. Because the subject is a noun (l'homme) and not a pronoun, you must state the noun first, then the verb (voit), and finally attach a matching pronoun (il) with a hyphen.

Why can't we just invert the noun and verb directly and say À peine voit l'homme la comète?

In French, you cannot invert a noun directly with a verb when using these sentence-initial adverbs. Simple inversion (verb + subject) is generally only for pronouns. For a noun, you must always use the complex inversion pattern: noun + verb + pronoun.

What is the purpose of qu' before elle?

It is part of the fixed expression À peine... que... which translates to barely... when... or hardly... than.... The que (contracted to qu' before elle) bridges the two clauses, showing that the comet disappears the very moment it is seen.

Is this complex inversion used in everyday spoken French?

Starting a sentence with À peine and using complex inversion is quite formal and mostly found in literature or careful speech. In everyday conversation, a French speaker would likely keep standard word order and move the adverb after the verb: L'homme voit à peine la comète qu'elle disparaît.