The theme of the song is, "nothing can compare to love." This the theme because, the speaker refers to the space as a comparison to his compassion towards his lover. Another example why this is the theme of the song is, he says, "in other words, hold my hand." Which he states after he talks about going to the moon, and singing among the stars. There he is indirectly comparing his love to wanting to interact with space, hence the theme. Therefore the theme of the song is, "nothing can compare to love."