The poem is divided into three stanzas of six lines each, with an ABABAB rhyme scheme. The rhyme scheme is pretty tidy, but what's up with the meter? The "meter" of a poem refers to the rhythm of stressed and unstressed syllables. Hold on – before you tune out, we'll explain.
OK in terms of meter here, we've said that the poem is written in iambic tetrameter. But what the heck does that mean as well? "Iambic" refers to the pattern of stresses in the line. An "iamb" is an unstressed syllable, followed by a stressed syllable: da-DUM. "Tetrameter" means that there are four ("tetra") iambs in the line: da-DUM da-DUM da-DUM da-DUM. Easy, right? Let's look at those iambs in action…
She walks in beauty, like the night
Of cloudless climes and starry skies;
If we bold the syllables that you'd naturally stress, you'll see what we mean:
She walks in beau-ty, like the night
Of cloud-less climes and star-ry skies;
And look – there are four bold syllables per line: four iambs = iambic tetrameter. There you go.
You hardly notice the iambic rhythm as you're reading unless you know to look for it – you probably just notice that the rhythm of the words is very even and smooth. The only time you do notice the rhythm is when it changes. Check out lines 3 and 4:
And all that's best of dark and bright
Meet in her as-pect and her eyes.
Line 3 is regular iambic tetrameter – no problem. But look what happens in line 4! Instead of starting with an unstressed syllable like all the other lines in the poem, this one starts with a stressed syllable. This is what critics call a "metrical inversion," in which the usual pattern is inverted, or reversed. Why would Byron do this? No, he didn't mess up; he was too good of a craftsman to make a mistake like that. Every other line in the poem is steady iambic tetrameter, so you could argue that this one break in the rhythm calls attention to the steadiness of the rest of it. After all, this is a poem about a woman's effortless grace and beauty, so it makes sense that the poem's meter should sound just as effortless. There are other possible interpretations of this metrical inversion, though. What effect does it have on your reading?