The sources and uses of astronomical constants by E.M. Standish (Caltech/JPL)
We discuss the use of ephemerides based upon the independent variable, "Teph", and compares it with the use of ephemerides based upon the recent IAU-defined "TCB". Teph has been used over the past three decades for the ephemerides created at JPL, CfA, and IPA; it has been referred to, somewhat erroneously, as "ET" and or "TDB" in the past. Teph and TCB are mathematically equivalent; they are both relativistic coordinate times. Proper use of a Teph-based ephemeris should give results identical to those obtained using a TCB-based ephemeris. However, care must be taken in some circumstances, such as navigating a spacecraft in orbit around a remote planet while timing the dynamics on an earth-based clock. This paper discusses such situations.