Lord Byron compares the subject of his poem to the night:
She walks in beauty, like the night
Of cloudless climes and starry skies.
This poem is now so well known that it has, to some extent, become a victim of its own success, and readers often fail to notice the strange and striking nature of this image. Byron avoids comparing his beloved to sunlight or daytime, since he claims that the night is more beautiful than the day. This influences the type of cloud the reader envisages. A cloud in the sunlight might be white and pure, but a cloud at night is dark and serves only to obscure the beauty of the stars.
A clime is a region, considered principally in terms of its weather. The word is seldom used now, and was not particularly common even in the early nineteenth century, but someone going on holiday might claim to be "leaving for warmer climes." These climes, which resemble the woman in the poem, are cloudless, meaning that they are pure and clear, allowing the beauty of the stars to shine through. The simile, therefore, reflects the purity as well as the beauty of the subject, counteracting the fact that she is compared with night, since clarity is usually considered an attribute of day.