Relativistic time scales in the Solar system

TL;DR

This paper reviews the theoretical and practical aspects of relativistic time scales in the Solar system, detailing their definitions, interrelations, and providing transformation recipes and ephemerides for major bodies.

Contribution

It clarifies the IAU 2000 framework's definitions of relativistic time scales and offers practical transformation methods and online ephemerides for Solar system bodies.

Findings

Provides transformation recipes between TCB and local coordinate times.

Offers Chebyshev polynomial ephemerides for all major Solar system bodies.

Argues against scaling local coordinate times like TCL for the Moon.

Abstract

This paper summarizes theoretical definitions of the relativistic coordinate time scales introduced by the IAU 2000 framework as well as practical aspects of their use. It is argued that the IAU framework already defines relativistic local GCRS-like reference systems and the corresponding TCG-like coordinates times for each body of the Solar system. The interrelations between the coordinate times and the proper time of an observer are discussed. The arguments put forward that any scaling of the local coordinate times like TCL for the Moon is unreasonable. Practical recipes of the transformations between TCB and the local coordinate time scales (TCG, TCL, etc) are then discussed. Time ephemerides giving the transformation between TCB and the local coordinate times at the center of mass of the corresponding body are computed for all major bodies of the Solar system using INPOP19a. Those time ephemerides represented as a standard set of Chebyshev polynomials are available online.