See both Videos for a full understanding of this subject.
In this 26 minute video interview, Daniel Giamario talks about the history of constellations and origins of the signs and why there is NOT a 13th sign in astrology. Interview conducted by Shamanic Astrologer Tami Brunk.
This 15 minute video from Cayelin Castell provides a visual explanation of why there are only 12 zodiacal signs or season in western astrology including Shamanic Astrology. The sub-title is Why There Are NOT 13 Signs Now or Ever. This Video also shows, as well as explains, how the signs (or seasons) are related to the constellations now and how these signs shift through the constellations over time.
For More See these Articles
Why We Use Signs and Love the Constellations by Daniel Giamario
The Difference Between Signs and Constellations by Cayelin K Castell