This is the 14367th most frequent Spanish word.
vigilan
"They watch" or "they guard."
In this sentence, 'vigilan' is used in its primary meaning 'they watch/monitor' to indicate an active observation.
Los guardias vigilan las puertas del edificio.
The guards monitor the doors of the building.
'Vigilan' is used metaphorically here to describe stars as if they are guardians of the night.
Las estrellas vigilan desde el cielo sobre la noche tranquila.
The stars watch over the peaceful night from the sky.
Here, 'vigilan' expresses the act of supervising or ensuring something is done.