  We report on an analysis of high-precision, multi-colour photometric
observations of the rapidly-oscillating Ap (roAp) star $\alpha$ Cir. These
observations were obtained with the BRITE-Constellation, which is a coordinated
mission of five nanosatellites that collects continuous
millimagnitude-precision photometry of dozens of bright stars for up to 180
days at a time in two colours (Johnson B and R). BRITE stands for BRight Target
Explorer. The object $\alpha$ Cir is the brightest roAp star and an ideal
target for such investigations, facilitating the determination of oscillation
frequencies with high resolution. This star is bright enough for complementary
interferometry and time-resolved spectroscopy. Four BRITE satellites observed
$\alpha$ Cir for 146 d or 33 rotational cycles. Phasing the photometry
according to the 4.4790 d rotational period reveals qualitatively different
light variations in the two photometric bands. The phased red-band photometry
is in good agreement with previously-published WIRE data, showing a light curve
symmetric about phase 0.5 with a strong contribution from the first harmonic.
The phased blue-band data, in contrast, show an essentially sinusoidal
variation. We model both light curves with Bayesian Photometric Imaging, which
suggests the presence of two large-scale, photometrically bright (relative to
the surrounding photosphere) spots. We also examine the high-frequency
pulsation spectrum as encoded in the BRITE photometry. Our analysis establishes
the stability of the main pulsation frequency over the last 20 years, confirms
the presence of frequency f7, which was not detected (or the mode not excited)
prior to 2006, and excludes quadrupolar modes for the main pulsation frequency.
