CMB dipole represents the largest anisotropy, which is in the first spherical harmonic (ℓ = 1), a cosine function. The amplitude of CMB dipole is around 3.3621 ± 0.0010 mK. The CMB dipole moment is interpreted as the peculiar motion of the Earth relative to the CMB. Its amplitude depends on the time due to the Earth's orbit about the barycenter of the solar system. This enables us to add a time-dependent term to the dipole expression. The modulation of this term is 1 year, which fits the observation done by COBE FIRAS. The dipole moment does not encode any primordial information.