What an ephemeris is
An ephemeris is a table of where the Sun, Moon and planets are on a series of dates. The word comes from the Greek for daily, and for centuries it was a printed book of numbers that sailors, astronomers and astrologers kept close at hand.
Before computers, astrologers calculated a chart by looking up positions for the nearest noon or midnight in an ephemeris and working out the difference by hand. Today the same numbers can be computed on the spot, but the table format is still the quickest way to scan a whole month.
How to read our table
Each row is one day, at 00:00 UTC. Each column is a body: Sun, Moon, Mercury, Venus, Mars, Jupiter, Saturn, Uranus, Neptune, Pluto and the true node. A position such as 14 Aries 22 means 14 degrees and 22 arcminutes into Aries.
An R beside a value means the planet appears to move backward on that day. When the R disappears, the planet has turned direct again. The Sun and Moon never carry an R, and the node's average motion is backward.
Why 00:00 UTC
A table has to be fixed to one clock time, and astronomers use Coordinated Universal Time, the modern successor to Greenwich time. Midnight UTC is 7 or 8 p.m. the previous evening on the US East Coast and 4 or 5 p.m. on the West Coast, depending on daylight saving time.
For the slow planets this hardly matters. For the Moon it matters a lot, since it moves about 13 degrees a day, so for a precise Moon position use the birth chart tool, which calculates for an exact minute.
The true node and the mean node
The lunar nodes are the two points where the Moon's orbit crosses the Sun's apparent path. The mean node smooths out the motion into a steady backward drift of about one full circle in 18.6 years. The true node follows the actual, wobbling position, and on some days it briefly moves forward.
We list the true node. You can read more about its meaning in the North Node calculator.
Where the numbers come from
We compute every value with Astronomy Engine, an open-source library based on modern planetary theory, accurate to about one arcminute. Positions are geocentric and tropical, measured from the spring equinox point, which is the standard for Western astrology. Details are on our method page.