  The motion of an observer in the rest frame of the cosmic 21-cm background
induces an anisotropy in the observed background, even when the background is
isotropic. The induced anisotropy includes a dipole and a quadrupole, in the
order decreasing in amplitude. If observed, these multipole anisotropies can be
used as additional probes of the spectral shape of the global 21-cm background
for mitigating the ambiguity in the monopole spectrum probed by single-element
radio telescopes such as EDGES and SARAS. This could also help with
understanding the astrophysical and cosmological processes that occurred during
the cosmic dawn and the epoch of reionization, and even improving on the
estimation of the solar velocity and the foreground spectra. Here, we study the
feasibility of such observations and present science drivers for the
measurement of the 21-cm dipole and quadrupole.
