  We present high-accuracy spectroscopy data of line strengths, transition
probabilities and oscillator strengths for the allowed transitions among the
$nS_{1/2}$, $nP_{1/2,3/2}$ and $n'D_{3/2,5/2}$ states with $n=5$ to $10$ and
$n'=4$ to $10$ of the Rb-isoelectronic Zr (Zr IV) and Nb (Nb V) ions.
%\textcolor{red}{except for a few transitions that seem to be unreliable.} They
can serve to analyse various astrophysical phenomena undergoing inside the
heavenly bodies containing Zr and Nb elements. Since there is a lack of precise
observational and calculated data for the spectroscopic properties in the above
ions, their accurate determinations are of immense interest. The literature
data, that are available only for a few selected low-lying transitions, have
large discrepancies and they cannot be used reliably for the above purpose.
After accounting for electron interactions through random phase approximation,
Br\"uckner orbitals, structural radiations and normalizations of wave functions
in the relativistic many-body methods, we have evaluated the electric dipole
amplitudes precisely. Combining these values with the observed wavelengths, the
above transition properties and lifetimes of a number of excited states of the
Zr IV and Nb V ions are determined and compared with the literature data.
