is there such a thing as Gnostic astrology?
I'm not 100% sure about this, but I'm fairly sure there is such a thing, and that the Templar Knights followed it. Honestly, you should just Google it.
Here's what a gnostic text called the Song of God says:
37.But in the night did Adamilus teach to both men and women the movement of the stars throughout the seasons of the year; and the phases of the moon did he likewise teach; and to the greater stars did Adamilus give names, and with his finger did Adamilus trace the constellations through the dark and twinkling skies.
38.For Adamilus used the constellations to tell the stories of God and Heaven and Hodos Alea, of Kronus and Yoshibeth, of Eidos and Areta, and the mysteries of Janmoleah;
39.To fill the minds of all which heard with dreams and wonders beyond the mortal man, yet being themselves within his reach if he would reach forth beyond himself to touch them.
~4th Endwoment 7:37-39
You can learn more at: http://www.truegnosticchurch.org/basic_beliefs.html
I think you'll really like the symbol they use if you are interested in astrology. A lot of symbolism in it.