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What it is

An ephemeris is a set of tables listing the exact positions of the Sun, Moon, and planets — usually in zodiac longitude — for every day of a given period. Think of it as a look-up book for "where was everything on this date?" Astrologers once used printed ephemerides to cast charts by hand, copying out each degree and noting every retrograde before doing the math.

The word comes from the Greek for "daily record," which is exactly what it is: a daily log of planetary positions in the past, present, and future. Modern ephemerides are generated by precision software such as the Swiss Ephemeris, which is built on NASA's JPL planetary data and covers thousands of years down to a tiny fraction of an arcsecond.

How to read it

A daily ephemeris is laid out as a grid: one row per day, with columns for the Sun, Moon, each planet, and often the lunar nodes, Chiron, and similar points. Each entry shows a planet's sign and degree — like "Mercury 22° Virgo" — plus a letter marking its motion, with R standing for retrograde. Column by column, you can trace a planet's path, watch it slow down, station, and turn direction.

For reading purposes, the ephemeris is how you locate transits by hand: look up the positions for today and compare them with the degrees in someone's natal chart. When a transiting planet sits on or near a natal point, that is an active transit. You can also use an ephemeris to run a progression — adding one day per year of life — and read the progressed positions straight off the table.

What it means in practice

In practice you almost never open a paper ephemeris: chart software computes positions automatically, and the Swiss Ephemeris runs silently in the background of most astrology apps. Still, understanding what an ephemeris is helps. It demystifies where charts come from, and it makes you less likely to treat generated numbers as magic. It is also handy for studying cycles — Mercury retrograde dates, eclipse times, Jupiter's sign changes — because the ephemeris makes the pattern of any planet's motion visible at a glance.

How it connects

The ephemeris is the shared raw data behind several techniques. Transits are read directly from daily positions, progressions come from advancing the same tables by one day per year, and a solar return is cast for the moment the ephemeris shows the Sun back at its natal degree. The two zodiacs — tropical and sidereal — are simply two ways of expressing the same ephemeris positions, with the sidereal offset, the ayanamsa, subtracted.