  Phase curves and secondary eclipses of gaseous exoplanets are diagnostic of
atmospheric composition and meteorology, and the long observational baseline
and high photometric precision from the Kepler Mission make its dataset
well-suited for exploring phase curve variability, which provides additional
insights into atmospheric dynamics. Observations of the hot Jupiter Kepler-76b
span more than 1,000 days, providing an ideal dataset to search for atmospheric
variability. In this study, we find that Kepler-76b's secondary eclipse, with a
depth of $87 \pm 6$ parts-per-million (ppm), corresponds to an effective
temperature of 2,830$^{+50}_{-30}$ K. Our results also show clear indications
of variability in Kepler-76b's atmospheric emission and reflectivity, with the
phase curve amplitude typically $50.5 \pm 1.3$ ppm but varying between 35 and
70 ppm over tens of days. As is common for hot Jupiters, Kepler-76b's phase
curve shows a discernible offset of $\left( 9 \pm 1.3 \right)^\circ$ eastward
of the sub-stellar point and varying in concert with the amplitude. These
variations may arise from the advance and retreat of thermal structures and
cloud formations in Kepler-76b's atmosphere; the resulting thermal
perturbations may couple with the super-rotation expected to transport
aerosols, giving rise to a feedback loop. Looking forward, the TESS Mission can
provide new insight into planetary atmospheres, with good prospects to observe
both secondary eclipses and phase curves among targets from the mission. TESS's
increased sensitivity in red wavelengths as compared to Kepler means that it
will probably probe different aspects of planetary atmospheres.
