Get out the microscope, because we’re going through this poem line-by-line.
She walks in beauty, like the night
Of cloudless climes and starry skies;
- An unnamed woman "walks in beauty." This is an odd way of saying that she's beautiful, isn't it? "Walk[ing] in beauty" makes her beauty seem more dynamic – as though it's partly her movement and the spring in her step that make her beautiful. She's not just a pretty face in a portrait; it's the whole living, breathing, "walk[ing]" woman that's beautiful.
- Her beauty is compared to "night." This seems strange – night is dark, right? Aren't beautiful women usually compared to "a summer's day"? (That would be Shakespeare's Sonnet 18, in case you were wondering).
- But the featured woman isn't just compared to any "night," she's compared to a night in a place where there are no clouds and lots of stars. We suppose that means she has a very clear and lovely complexion? Or perhaps being "cloudless" has more to do with her personality – her conscience might be as clear as a "cloudless" sky.
- You see "starry skies" at night, but the brightness of the stars relieves the darkness of the night. This is the first hint of a contrast between light and dark in the poem.
- There's some pretty sweet alliteration in these lines. You might want to head over to the "Symbols" section for more on that before moving forward.
And all that's best of dark and bright
Meet in her aspect and her eyes:
- The contrast between light and dark that was first brought up by the "starry skies" in line 2 is repeated and developed in line 3.
- Everything that is great about both "dark" and "bright" come together in this woman. Essentially, she's got the best of both.
- Her "aspect" can mean both her facial expression and her overall appearance.
- So her whole appearance and especially her "eyes" create some kind of harmony between "dark" and "bright."
- If this seems weird to you, think of a really beautiful person who has dark eyes that always seem to sparkle – or someone whose eye color contrasts with his or her hair color in an attractive way. That's what Byron's talking about – contrast that creates beauty and harmony.
- Byron's setting up a binary, or opposition, between "bright" and "dark," but it's important to realize that neither is considered better or worse than the other. Both have aspects that are "best."
Thus mellowed to that tender light
Which heaven to gaudy day denies.
- Everything that's great about both "dark and bright" (line 3) is "mellow'd," or toned down to something that's more "tender" and less intense than the light you get during the day.
- Since Byron has been talking about night, try thinking about starlight or moonlight – that would be a "tender light" that is less "gaudy," or bright and blinding, than the light you get during the day.