s or sec), corresponding to one 86,000th part of the mean solar day, i.e. the duration of rotation, about its own axis, of an ideal Earth describing a circle round the Sun in one year, at a constant speed and in the plane of the Equator.
(s or sec; corresponding; to one 86,000th part of the mean solar day, i.e. the duration of rotation, about its own axis, of an ideal Earth) (an ideal Earth; describing round; a circle)
s or sec an ideal Earth
corresponding describing round
to one 86,000th part of the mean solar day, i.e. the duration of rotation, about its own axis, of an ideal Earth
a circle