by Vladimir ZHAROV, Dr. Sc. (Phys. & Math.), Gravimetry Laboratory Head, P. Shternberg Astronomical Institute, Lomonosov Moscow State University For ages man has been using rotation of the earth in time measurements. Found to be irregular since the atomic clock entered the stage in the mid-20th century, it depends on many processes unfolding within our planet, in its oceans and atmosphere. Relevant information goes far beyond pure science alone-it matters a good deal for hands-on problem solving, too. Now why is our planet spinning irregularly and why is humankind spending so much for research into the phenomenon? Before answering these and other questions, let us first turn to the history of astronomy, a science as old as the human world. From the very outset it was concerned with the following objectives: fixing an observer's position; establishing the location of a place on earth; taking celestial fixes to obtain a position (and determine the time of religious and historic events). Economic considerations, too, made it necessary to have an exact calendar based on astronomical observations of the sun, moon and stars. Today these problems are being tackled by astrometry, one of the disciplines within astronomy. From a large number of cuneiform-script clay tablets found in Mesopotamia (a flat country between the Tigris and the Euphrates) we know for sure: even at that time (4 - 3 thousand years B. C.) high priests indulged in star-gazing. They determined the periods of solar and lunar eclipses and learned how to predict these natural phenomena. Babylonians (Babylonia was an ancient empire in southern Mesopotamia that flourished early in the second millennium B. C. in what is now Iraq) developed a sexagesimal (base - 60) system of calculus and a lunar-solar calendar. The nascent science of astronomy owed much to high priests of ancient Egypt, too. The welfare of that country depended on the Nile and its regular overflows that brought fertile silt onto cultiva ... Read more