Jane Taylor wrote this as part of a longer poem called "The Star"; only the opening verses are commonly sung today, and this is the one everybody knows. Its wondering tone and the simple wonder-what-you-are line make it a gentle way to end the day looking up at the sky, real or imagined.
From Mother Goose / Nursery Rhymes (traditional). See the whole collection.
Twinkle, twinkle, little star,
How I wonder what you are!
Up above the world so high,
Like a diamond in the sky.
When the blazing sun is gone,
When he nothing shines upon,
Then you show your little light,
Twinkle, twinkle, all the night.
When the traveller in the dark
Thanks you for your tiny spark:
How could he see where to go
If you did not twinkle so?
In the dark blue sky you keep,
Often through my curtains peep,
For you never shut your eye,
Till the sun is in the sky.
As your bright and tiny spark
Lights the traveller in the dark,
Though I know not what you are,
Twinkle, twinkle, little star.
Public domain. Text from The Little Mother Goose (illustrated by Jessie Willcox Smith, 1912), via Project Gutenberg. View the source edition