In the Confessio attributed to Patrick, the author has Patrick say that after he was sold into captivity and taken to Ireland, Patrick spent time tending sheep (see Section 16 of the Confessio, linked above). The constellation Sagittarius often plays the role of a young shepherd who tends to sheep or goats, owing to the slender appearance of the constellation itself (see star chart above) and to the fact that Sagittarius is located immediately adjacent to the Goat of Capricorn in the night sky (not visible in the chart above, but located immediately to the right of Sagittarius as the image is oriented above -- that is, immediately to the east of Sagittarius).
Thus, Joseph as a youth (sold into captivity in Egypt) is associated with Sagittarius, and Patrick as a youth (sold into captivity in Ireland) is also associated with Sagittarius. As I have demonstrated elsewhere, the god Dionysus (who was also captured by pirates in one episode) can also be shown to have been associated with both Sagittarius and also Capricorn in his youth, as a way of hiding from the wrath of the goddess Hera.
When Patrick becomes a bishop, however, he can be shown beyond any doubt to be associated with the pivotal figure of Ophiuchus (and, intriguingly enough, as I have also shown with abundant supporting evidence elsewhere, both Joseph and also the god Dionysus can be shown to be associated with Ophiuchus as well).
Depictions of St Patrick almost universally depict the bishop standing atop one or more serpents, as can be seen in both of the depictions in the star-chart above. Standing above or atop a serpent or multiple serpents (or atop a serpent with multiple heads) is a very strong indication of association with the constellation Ophiuchus, because Ophiuchus in the sky is positioned directly above as if standing atop the constellation Scorpio -- and Scorpio often plays a serpent in ancient myth and ancient scriptures, including a serpent with multiple heads.
Additionally, St Patrick is usually depicted carrying a staff, sometimes a crook-staff, and Ophiuchus figures in myth often carry rods, staffs, or spears, for reasons which should be obvious from the outline of the constellation itself shown in the star chart above. Note that Moses is also a figure who can be confidently shown to be associated with Ophiuchus, and Moses of course also carries a staff -- and one which can turn into a serpent. There are some depictions of St Patrick in which the serpent at his feet is actually winding its way up the base of Patrick's staff.
Patrick is also often shown with his hand in a gesture associated with the "serpent's head" feature of the constellation Ophiuchus -- with thumb and two fingers raised. The top of the "serpent's head" of Ophiuchus (on the right side of the constellation, as seen in the star chart above -- that is to say, the west side of Ophiuchus) is formed by three stars:
