The Barddas of Iolo Morganwg, Vol. I., ed. by J. Williams Ab Ithel, , at sacred-texts.com
There are three kinds of stars: fixed stars, which keep their places, and are also called stationary stars; erratic stars, which are called planets, and are fifteen in number, seven 2 being always visible, and eight invisible, except very seldom, because they revolve within and beyond the Galaxy; and the third are irregular stars, which are called comets, and nothing is known of their place, number, and time, nor are they themselves known, except on occasions of chance, and in the course of ages.
From Bardism--Fragments about the months and other things.
403:2 p. 402 Seven of the Planets are mentioned in a poem of Taliesin, called "Canu y Byd Mawr," or the Song of the Great World. Myv. Arch. v. i. p. 25.