What is the poet comparing moon to in was a ghostly galeleon tossed upon cloudy seas highwayman?

In the poem "Highwayman," the moon is compared to a "ghostly galeleon tossed upon cloudy seas." A galeleon is a type of sailing ship that was used in the 16th and 17th centuries. The poet is comparing the moon to a ghost ship because it appears to be floating through the sky like a ship on the ocean. The clouds are compared to the sea, and the moonlight is compared to the waves. This comparison creates a sense of mystery and beauty, and it helps to set the mood for the poem.