  The time in an atomic clock in motion is discussed using the analogy of a
sing around sound source. Sing around frequency is modified according to the
motion of the sing around sound source, using the Lorentz transformation
equation. Thus, if we use the sing around frequency as a reference, we can
define the reference time. We propose that the time delay of an atomic clock in
motion be derived using the sing around method. In this letter, we show that
time is defined by a combination of light speed and motion.
