Remarks concerning reference frames

Twenty years ago I published A Catalog of 939 PZT Stars on the System of the FK4. At the time it was well received and indeed it did tighten up various PZT results. As I recall, the catalog, among other things, confirmed an empirical relationship between the Richmond, Florida and Washington, DC instruments which had been derived by Prof. Markowitz. In any event, I planned to follow up on this work, but an assignment to El Leoncito, Argentina intervened. Perhaps it was just as well because other things were happening. Astronauts were soon tramping about the moon and littering up the place with a used car and something called a retro-reflector. Radio astronomers were constantly refining the astrometric potential of their interferometric techniques; strange, high-z, starlike objects had been detected a few years earlier; shiny, new satellites were launched; and shortly the science of determining Earth Rotation Parameters (ERP), or “Orientation Parameters” if you prefer, was to explode with vitality and to reach precisions and accuracies never before achieved. As a matter of fact, the new riches became so numerous that, like the proverbial kid in the candy store, the ERP community was, to some extent, forced to choose among some of them. Thus was born the MERIT campaign.