1. Solar and sidereal times Universal Time (UT): is defined by the greenwich Notice Ir angle augmented by 12 hours of a fictitious Both solar and sidereal time are not uniform since mly orbiting in the equatorial plane(p. 35) the angular velocity we is not constant. Changes in the polar moment of inertia exerted Sidereal Time(ST: is defined by the hor by tidal deformation the vernal Taking the mean equinox as the reference leads to Oscillations of the earth's rotational axis itself 2. Dynamic Times Dynamic Times: The time systems derived from planetary onions in the solar system are called dynamic times In 1991. the International Astronomical Unior yeentrio Dynamic Time(BDT): is an inertial time introduced the term Terrestrial Time(r)to stem 1 Newtonian sense and pr ovides the time TDT. Furthermore, the terminology of coordinate variable in the equations of motion. according to the theory of general relativity was merly called ephemeris time and serves for the integration of the differential equations for the orbital motion of satellites around the earth 3. Atomic Times 3.2 Conversions Dynamic Time System is achieved by the use of atomic time UTC S c second. but to k The unit of the system is the keep the system clos e=1.0027379093Um1+uo+△cos UTI and integer leap seconds are inserted at distinct epochs 1. The first term. the different scales of solar and sidereal GPS Time is also related to the atomic time system 2. The quantity Do represents the actual sidereal time at Naval Observatory (USNO) 3. The third term: the projection of Ao onto the equator and 2. GPS time system nominally has a constant offset of considers the effect of nutation seconds with iat 3. GPS Time was coincident with Utc at the Gp standard epoch 1980, January 6. 05 1. Solar and Sidereal Times Universal Time (UT): is defined by the Greenwich hour angle augmented by 12 hours of a fictitious sun uniformly orbiting in the equatorial plane (p. 35). Sidereal Time(ST): is defined by the hour angle of the vernal equinox. Taking the mean equinox as the reference leads to mean sidereal time and using the true equinox as a reference yields true or apparent sidereal time (p. 35). Both solar and sidereal time are not uniform since the angular velocity wE is not constant. • Changes in the polar moment of inertia exerted by tidal deformation • Other mass transports • Oscillations of the earth's rotational axis itself Notice 2. Dynamic Times Dynamic Times: The time systems derived from planetary motions in the solar system are called dynamic times. Barycentrio Dynamic Time (BDT): is an inertial time system in the Newtonian sense and provides the time variable in the equations of motion. Quasi-inertial Terrestrial Dynamic Time (TDT): was formerly called ephemeris time and serves for the integration of the differential equations for the orbital motion of satellites around the earth. In 1991, the International Astronomical Union (IAU) introduced the term Terrestrial Time (TT) to replace TDT. Furthermore, the terminology of coordinate times according to the theory of general relativity was introduced 3. Atomic Times Dynamic Time System is achieved by the use of atomic time scales. UTC System is a compromise. The unit of the system is the atomic second, but to keep the system close to UT1 and approximate civil time, integer leap seconds are inserted at distinct epochs. GPS Time is also related to the atomic time system. 1. GPS time is referenced to UTC as maintained by the U.S. Naval Observatory (USNO). 2. GPS time system nominally has a constant offset of 19 seconds with IAT. 3. GPS Time was coincident with UTC at the GPS standard epoch 1980, January 6.d0. 3.2 Conversions The conversion between the times is achieved by the formula Θ0 = 1.0027379093 UT1 + υ0 + ∆φcosε 1. The first term: the different scales of solar and sidereal time, 2. The quantity υ0 represents the actual sidereal time at Greenwich midnight (i.e., 0h UT). 3. The third term: the projection of ∆φ onto the equator and considers the effect of nutation