The accelerated expansion of the Universe, attributed to the existence of dark energy, was discovered nearly two decades ago using distance measurements of Type Ia supernovae. To find the supernovae, image differencing was used targeting small parts of the sky, with just several thousand galaxies observed a few weeks apart. Since then, technological advances have allowed us to drastically increase the science reach of time-domain astronomy: the new generation of optical cameras can image the entire observable sky in a single night. We are starting to discover very rare phenomena, and to explore new time scales for transient phenomena, allowing us to chart new physics territories.