siderealist

A siderealist is a person who adheres to or promotes sidereal concepts in timekeeping, astronomy, or astrology. The term is derived from sidereal, relating to the stars, with the agentive suffix -ist. Because “siderealist” is not a standardized title, its exact meaning can vary by discipline and community.

In astronomy and timekeeping, a siderealist may emphasize the use of sidereal time, which measures Earth's rotation relative to fixed stars rather than the Sun. Sidereal time underpins celestial coordinate systems that use right ascension and declination. Practically, advocates of sidereal time emphasize star-based celestial mapping and may align observational schedules with stellar phenomena rather than solar-based cycles.

In astrology, siderealists follow the sidereal zodiac, where the zodiac signs are aligned with the current positions of the fixed stars. This is in contrast to tropical astrology, which ties the zodiac to the seasons. The sidereal approach is common in Hindu astrology (Jyotisha) and is also used by some Western astrologers who prefer stars-based calculations. The term does not denote a single, uniform school but rather a label for practitioners who emphasize star-based reference frames.

Because the term is variably used, it is best understood from context: it may refer to adherence to sidereal time in astronomy, to the use of the sidereal zodiac in astrology, or more generally to any star-based frame of reference. See also sidereal time, sidereal zodiac, tropical zodiac, and Jyotisha.