Rashi tells us that the Egyptian astrologers had difficulty ascertaining
whether the savior of Klal Yisroel would be an Egyptian or a Jew, and for
this reason Pharaoh, out of an abundance of caution, decreed that all boys
born, even Egyptians, be drowned on that particular day. (1:22)
This suggests that the Egyptian astrologers were unclear or unsure of the
signs they were seeing in the stars. We do not find elsewhere that they
were aware of uncertainty about their insights - why was this one hard for
them to figure out?
Basia bas Pharaoh raised Moshe. (2:10). The gemoro (Sanhedrin 19b) says
that one who raises an orphan child is like that child's natural parent.
In fact one of the proofs the gemoro uses to support this idea is a pasuk
in Divrei Hayamim I (Ch 4) describing Basia bas Pharaoh as having given
birth to Moshe; she is so described because she raised him.
Perhaps this was the source of the astrologers' mindset. They were not
confused; they were right on target in what they perceived - Moshe Rabbenu
in fact was the product of two upbringings, one Jewish (natural) and one
Egyptian (adopted). [As an aside, it is always fascinating to dwell upon
the notion that the greatest Jewish leader was raised in a non-Jewish
home. A midrash says that, like Moshe, Moshiach will come from the Edom
culture he eventually will overturn.]
Similarly, Rashi says in Parshas Vayeshev (39:1) that the wife of Potiphar
understood astrologically that either she or her daughter was destined to
bear Yosef's children. Yet Chazal say (Maseches Sofrim 21:9) that
Potiphar's daughter (who did become Yosef's wife) was the daughter of
Dinah who was adopted by Potiphar - why would there be an astrological
reality to this girl being Potiphar's daughter, given that she
was 'merely' adopted? Rather, an adopted child is like a natural child,
and not just down here on earth but even in the stars and in the essence
of the relationship.