Astrology has been a topic of debate among Jews for over 2000 years. While not a Jewish practice or teaching as such, astrology made its way into Jewish thought, as can be seen in the many references to it in the Talmud. Astrological statements became accepted and worthy of debate and discussion by Torah scholars. Opinions varied: some rabbis rejected the validity of astrology; others accepted its validity but forbid practicing it; still others thought its practice to be meaningful and permitted. In modern times, as science has rejected the validity of astrology, many Jewish thinkers have similarly rejected it; though some continue to defend the pro-astrology views that were common among pre-modern Jews.
In pre-modern Hebrew, astrology was known as hokmat ha-mazalot (חוכמת המזלות), "the science of the constellations".
In the Hebrew Bible
As far as can be known from the Bible, astrology was not practiced in ancient Israel during the First Temple period. The Torah contains no references to astrology, and in the Nevi'im (Prophets) and Ketuvim (Writings), only obscure references to Babylonian astrologers exist.
Two commandments in the Torah have been understood by some later authorities as a basis to forbid astrology:
These commandments are understood by some rabbinic authorities as forbidding astrology, while others limit these mitzvot to other forms of soothsaying, and thus view astrology as permissible.
The Hebrew word mazalot, which literally means "constellations", is used twice in the Hebrew Bible. Specific constellations are also mentioned, such as Orion (named "Kesil" "כסיל", literally: "fool"; possibly etymologically connected with "Kislev", the name for the ninth month of the Hebrew calendar (i.e. November–December), which, in turn, may derive from the Hebrew root K-S-L as in the words "kesel, kisla" (כֵּסֶל, כִּסְלָה, hope, positiveness), that is, hope for winter rains), which is mentioned three times: Job 9:9 ("He is the maker of the Bear and Orion"), Job 38:31 ("Can you loosen Orion's belt?"), and Amos 5:8 ("He who made the Pleiades and Orion").
The prophets scoffed at "star-gazers" (hoverei ha-shamayim) in and . Astrologers from Babylon were called Kasdim/Kasdin (Chaldeans) in the Book of Daniel. In rabbinic literature, the term Chaldeans later was often used as a synonym with those who practiced astrology.
In the Second Temple period
For most of the Second Temple period, discussion of the planets in Jewish literature was extremely rare. Some historians hold that astrology slowly made its way into the Jewish community through syncretism with ancient Hellenistic culture. In prophesizing on the destruction of the Temple, the Sibylline oracles praise Jewish ancestors who "have no concern about the course of the sun's revolution, nor the moon's [..] Nor soothsayers, nor wizards, nor enchanters [...] Neither do they astrologize with skill of the Chaldeans, nor astronomize; O For these are all deceptive"; although the author of the Encyclopaedia Judaica article on astrology holds that this view is mistaken.
The early historian Josephus censures the people for ignoring what he thought were signs foreshadowing the destruction of the Temple in Jerusalem.
There are many references to astrology in the apocrypha. The Book of Jubilees said that Abraham overcame the beliefs of astrologers by accepting one God.
In the Talmudic period
In early classical rabbinic works written in the land of Israel (Jerusalem Talmud and midrash compilations) astrologers are known as astrologos and astrologiyya. In early classical rabbinic works written in Babylonia, astrologers were called kaldiyyim, kalda'ei, and iztagninin.
Is astrology valid?
The most popular form of astrological belief in this period was to regard certain periods of time as lucky or unlucky. For example, Rabbi Yehoshua ben Levi listed the character traits associated with one's having been born on specific days of the week; R' Hanina dissented and said that character traits are determined by the planet under whose influence one was born. An announcement is found to the effect that it is dangerous to drink water on Tuesday and Friday evenings. Samuel of Nehardea, a physician and astrologer, taught that it was dangerous to bleed a patient on Tuesday (as well as on Monday or Thursday for a different reason), because Mars reigns at the midheaven. The new moon was likewise regarded as an unfavorable season for bleeding, as were also the third of the month and the day preceding a festival.
Ecclesiastes Rabbah states that the rulers of some non-Jewish nations were experts in astrology, and that King Solomon too had expertise in this realm.