free mode in the motion of the Earth's rotation axis with respect to the Earth, due to non-alignment of the rotation axis of the inner core with respect to the mantle; the period is retrograde diurnal in the terrestrial frame and prograde long-period in the celestial frame.

Source: IERS Technical Note 36: Glossary (PDF, 244KB, Not barrier-free file.) of the IERS Conventions (2010)

a set of mathematical expressions for angles used to describe orbital parameters of solar system objects used in precession/nutation models.

Source: IERS Technical Note 36: Glossary (PDF, 244KB, Not barrier-free file.) of the IERS Conventions (2010)

Acronym: FK5

The FK5 is a catalogue of positions and proper motions of fundamental stars.

Until the adoption of the International Celestial Reference Frame, the FK5 was the basis for all celestial positions.

Related terms:

• International Celestial Reference Frame (ICRF)

Related links:

• The Fifth Fundamental Catalogue (scan of printed version)