IX.3. Calculations

This option enables one to calculate length of projections of geocentric radius-vector of any point on the Earth surface on the equatorial plane and on the Earth rotation axis, dxy and dz, correspondingly. The result is expressed in parts of the Earth equatorial radius. These values are functions of the geographical (geodesic) latitude and the height of the point above the sea level. Precision of computed values of dxy and dz depends on the number of correct decimals in the latitude, and they are displayed with two decimals more than it is introduced for latitude in degrees. When computing dxy and dz the value of equatorial radius equal to 6378.137 km and the value of oblateness of the Earth spheroid equal to 1/298.2572 are used. The computed values can be used for editing the observatory list.

The option also permits to solve the reverse problem — to calculate approximate values of observatory latitude and its height above the sea level depending on the introduced values of dxy and dz. The computed value of latitude is displayed with two decimals less than it is introduced into data fields for dxy and dz. Rounding off the value of height also depends on number of decimals in dxy and dz.

If you click on some entry in the observatory list (and by doing so, mark off corresponding observatory) and then select Calculate item in drop-down menu, then values of dxy and dz for that observatory will be entered into proper data fields of the present options. It is sufficient to click on Run to obtain latitude of the observatory and its height above the sea level.

It should be mentioned that low precision of dxy and dz for some observatories in the list maintained by MPC leads to negative value of height above the sea level for some of them. It is nothing more than an artifact.