ROME

Rome took the Greek pantheon almost wholesale through the interpretatio romana, identifying its own gods with the Olympians: Iuppiter with Zeus, Venus with Aphrodite, Mars with Ares. But the names that matter for astrology are the Roman ones. Mercury, Venus, Mars, Jupiter, and Saturn are simply these gods, and they reach every modern European language through the Roman calendar, which makes Rome the most direct ancestor of the planetary vocabulary the rest of this app translates away from.

Roman astrology was a high-stakes civic practice rather than a private comfort. Emperors employed astrologers and also feared them; the expulsions of astrologers from the city under Tiberius and others show how seriously the readings of the sky were taken. The seven-day planetary week that still orders the calendar is a Roman inheritance from the Hellenistic synthesis, each day named for one of the seven gods who name the planets; this app enrolls three further bodies beside them, received rather than calendared, and says so wherever they appear.