It’s worth noting that Japanese words have more syllables on average than English words do. So in effect, seventeen syllables in English can carry more meaning. In a way, English haiku are cheating.
To better represent the sparsity of thought in a Japanese haiku, a literature professor named Robert Kelly invented the lune, a thirteen-syllable poem divided five/three/five. He named this form the lune, because the right side of most examples creates a crescent shape, like a crescent moon.
Here’s an example I posted to Twitter and Facebook a few days ago.
if not for the birds
I’d not know
that I cannot fly
(For what it’s worth, the lune is probably my favorite form of poem. And considering how much I love the sonnet, that’s saying something!)
Another fellow, named Jack Collum, was teaching this form to children, and slightly misremembered it. Instead of five/three/five syllables, he thought three/five/three words. This being somewhat easier for children to count, the form has stuck.
Note that because “lune” is an English word, two or more of these poems are “lunes.” By contrast, more than one haiku, senryu, or tanka become “two haiku,” “five senryu,” or “seventy-nine tanka,” for example.
I hope that this brief overview of these related forms has inspired you to write some of your own. Just remember to make each line stand at least somewhat on its own, rather than seeming like a sudden U-turn in the street, simply because you've run out of syllables. And try to have a significant change in thought, some measure of surprise, in one of the breaks. Your readers will appreciate the effort!
—Les