Ephemeris
Glossary · Last updated: 2026-07-26
An ephemeris (plural ephemerides) lists sky positions for dates and times. Astrology software interpolates these tables to find sign boundaries.
Without an ephemeris or equal orbital math, sign calculators would rely on hard-coded date ranges that drift near cusps.
Example: see it on a birth date
An ephemeris is a table of planet positions by date. For December 15, 2021 the Western sun sign is Sagittarius.
Our noon estimate puts the Moon in Mesha rashi that day. An ephemeris is the source table. A horoscope page is a reading built from positions like these.
Enter your own date on the Zodiac Sign Calculator.
Our methodology
Western and Indian Vedic positions on this site come from astronomical libraries with documented ayanamsa for sidereal work. See our calculator methodology hub for detail.
Related
Main reading and tools
These are the main reading and calculator pages. Use them for a daily note, a birth-sign tool, or a pair check.
- Today's Horoscope hubAll twelve Western sun-sign daily pages, plus links to the seven-tradition reader.
- Horoscope & Zodiac CompatibilityTwo birth dates for Western, Chinese, and Indian Vedic pairing, plus every sun-sign hub.
- Zodiac Sign CalculatorWestern sun sign from birth date, with element, modality, and ruler.
- Rising Sign CalculatorIndian Vedic Lagna estimate when you have birth date, time, and place.
- Moon Sign CalculatorIndian Vedic Janma Rashi and nakshatra when birth time and city are available.