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.