Word origin · etymology
Standardized epoch notation.
J denotes a Julian epoch and 2000 its year label; J2000.0 names a precisely defined astronomical reference instant.
How we know · epistemology
Reference epoch
The epoch is defined at a specified TT instant. A catalogue labeled J2000 still needs its frame and proper-motion information; an epoch label alone cannot place a star at another date.
Connected concepts
Terms used in this explanation
Mentioned in 2 other entries
These links connect subjects and terminology. They do not establish a shared historical origin.
Sources & provenance
Use the citations beside each section to distinguish a calculation convention, a historical teaching and an editorial example.