secular variation


secular variation

[′sek·yə·lər ‚ver·ē′ā·shən] (astronomy) A perturbation of the moon's motion caused by variations in the effect of the sun's gravitational attraction on the earth and moon as their relative distances from the sun vary during the synodic month. (geophysics) The changes, measured in hundreds of years, in the magnetic field of the earth. Also known as geomagnetic secular variation.