The second is currently defined as
A) 1/86,400 of a mean solar day.
B) 1/86,164 of a sidereal day.
C) 1/31,557,600 of the period of the Earth's rotation around the Sun.
D) the time required for light to travel 1/299,792,458 of a meter.
E) the time that it takes the radiation from a Cesium-133 atom to complete 9,192,631,770 cycles of oscillation.

Question

Quizplus · Accepted Answer

The second is currently defined as the time that it takes the radiation from a Cesium-133 atom to complete 9,192,631,770 cycles of oscillation. This definition is based on atomic time, which is more stable and accurate than observations of celestial objects (sidereal time) or the rotation of the Earth (solar time). Thus, choice E is the best answer.

The Second Is Currently Defined as