  The arrival time distribution of cosmic ray events is well suited to extract
information regarding sky anisotropies. For an experiment with nearly constant
exposure, the frequency resolution one can achieve is given by the inverse of
the time $T$ during which the data was recorded. For $T$ larger than one
calendar year the resolution becomes sufficient to resolve the sidereal and
diurnal frequencies. Using a Fourier expansion on a modified time parameter, we
show in this note that one can accurately extract sidereal modulations without
knowledge of the experimental coverage. This procedure also gives the full
frequency pattern of the event sample under studies which contains important
information about possible systematics entering in the sidereal analysis. We
also show how this method allows to correct for those systematics. Finally, we
show that a two dimensional analysis, in the form of the spherical harmonic
($Y_l^m$) decomposition, can be performed under the same conditions for all
$m\ne 0$.
