| Date Time Terminology |
| BCE |
Before Common Era |
| BCRS |
Barycentric Celestial Reference System
(Geocentric - GCRS) |
| BCT |
Barycentric Coordinate Time |
| CDC |
Century Date Change (19xx to 20xx etc.) |
| CST |
Central Standard Time (central part of USA) |
| EST |
Eastern Standard Time (eastern USA) |
| GAST |
Greenwich Apparent Sidereal Time |
| GAT |
Greenwich Apparent Time |
| GCRS |
Geocentric Celestial Reference System
(Barycentric - BCRS) |
| GCT |
Geocentric Coordinate Time
(aka
TCG) |
| GMT |
Greenwich Mean Time (same as
UTC) |
| GMST |
Greenwich Mean
Sidereal Time |
| GST |
Greenwich Sidereal Time |
| ICRF |
International Celestial Reference Frame |
| ICRS |
International Celestial Reference System |
| IDL |
International Date Line (line where the day begins) |
| IERS |
International Earth Rotation Service (established in 1987) |
| IRM |
IERS
Reference Meridian |
| ITRS |
International Terrestrial Reference System |
| LOD |
Length of Day (60 x 60 x 24 = 86,400 s) |
| MST |
Mountain Standard Time (mid-west part of USA) |
| PST |
Pacific Standard Time (pacific/western part of USA) |
| TCG |
Geocentric Coordinate Time |
| TDT |
Terrestrial Dynamical Time (time based on an atomic scale for astronomical computations) |
| TZO |
Time Zone Offset |
| UTC |
Coordinated Universal Time (same as
GMT) |