IVOA recommendation: Units in the VO

TL;DR

This paper presents a standardized syntax for representing units in the Virtual Observatory, aligning with international standards and ensuring compatibility with other parsers.

Contribution

It introduces a recommended syntax for VOUnits and a set of recognized and deprecated units consistent with global standards.

Findings

Defines a formal syntax for VOUnits

Provides machine-readable grammars for unit parsing

Ensures compatibility with existing standards

Abstract

This document describes a recommended syntax for writing the string representation of unit labels ("VOUnits"). In addition, it describes a set of recognised and deprecated units, which is as far as possible consistent with other relevant standards (BIPM, ISO/IEC and the IAU). The intention is that units written to conform to this specification will likely also be parsable by other well-known parsers. To this end, we include machine-readable grammars for other units syntaxes.