Data will be provided for a three year period from 1 January of the preceding year through 31 December of the following year. For dates outside of this range, see MICA.
Be sure to read the Notes section (on this page beyond the two forms) for definitions and additional details on the data.
Form A - U.S. Cities or Towns
Form B - Locations Worldwide
Sidereal time is equal to the hour angle of the catalog equinox and is a direct measure of the diurnal rotation of the Earth. Apparent sidereal time is defined by the intersection of the true equator of date with the ecliptic of date and is affected by the precession and nutation of the axis of the Earth. Mean sidereal time is measured against the mean equinox of date and is only affected by precession.
Equation of the Equinoxes
The Equation of the Equinoxes is equal to the apparent sidereal time minus the mean sidereal time.
Equation of Time
The Equation of Time is the difference apparent solar time minus mean solar time. To obtain this value for a specified time, calculate the apparent geocentric right ascension and declination of the Sun using the Geocentric Positions of Major Solar System Objects and Bright Stars service.