Ephemeris

An ephemeris (plural: ephemerides) is a table or dataset that lists the daily positions of the Sun, Moon, planets, and other celestial bodies at specific times. In astrology, it is the fundamental reference tool for calculating natal charts, transits, and other astrological events. Before computers, astrologers relied on printed ephemeris books; today, most chart calculation engines use digital ephemerides.

How it works

The ephemeris records the longitude (and often latitude) of each planet for every day, usually at midnight or noon Greenwich Mean Time. For example, on January 1, 2024, the Sun is at 10° Capricorn 15'. To calculate a birth chart, an astrologer looks up the planetary positions for the birth date and time, then adjusts for the time zone and location. Modern ephemerides also include additional data like retrograde periods, lunar phases, and eclipses.

In practice

When you read about a transit — say, "Jupiter enters Gemini" — that information comes from the ephemeris. In a personal reading, the ephemeris helps an astrologer see which planets are activating a specific point in your chart on a given day. For example, if transiting Mars is at 15° Aries and your natal Sun is at 15° Aries, that's a conjunction — a moment of heightened energy. You can explore your own transits by checking the Astraly calendar.