  We report the discovery of WASP-189b: an ultra-hot Jupiter in a 2.72-d
transiting orbit around the $V = 6.6$ A star WASP-189 (HR 5599). We detected
periodic dimmings in the star's lightcurve, first with the WASP-South survey
facility then with the TRAPPIST-South telescope. We confirmed that a planet is
the cause of those dimmings via line-profile tomography and radial-velocity
measurements using the HARPS and CORALIE spectrographs. Those reveal WASP-189b
to be an ultra-hot Jupiter ($M_{\rm P}$ = 2.13 $\pm$ 0.28 $M_{\rm Jup}$;
$R_{\rm P}$ = 1.374 $\pm$ 0.082 $R_{\rm Jup}$) in a polar orbit ($\lambda =
89.3 \pm 1.4^\circ$; $\Psi = 90.0 \pm 5.8^\circ$) around a rapidly rotating
A6IV-V star ($T_{\rm eff}$ = 8000 $\pm$ 100 K; $v_* \sin i_*$ $\approx$ 100
km\, s$^{-1}$). We calculate a predicted equilibrium temperature of $T_{\rm
eql}$ = 2641 $\pm$ 34 K, assuming zero albedo and efficient redistribution,
which is the third hottest for the known exoplanets. WASP-189 is the brightest
known host of a transiting hot Jupiter and the third-brightest known host of
any transiting exoplanet. We note that of the eight hot-Jupiter systems with
$T_{\rm eff}$ $>$ 7000 K, seven have strongly misaligned orbits, and two of the
three systems with $T_{\rm eff}$ $\geq$ 8000 K have polar orbits (the third is
aligned).
