Data Mining and Machine-Learning in Time-Domain Discovery & Classification

The changing heavens have played a central role in the scientific effort of astronomers for centuries. Galileo's synoptic observations of the moons of Jupiter and the phases of Venus starting in 1610, provided strong refutation of Ptolemaic cosmology. In more modern times, the discovery of a relationship between period and luminosity in some pulsational variable stars led to the inference of the size of the Milky Way, the distance scale to the nearest galaxies, and the expansion of the Universe. Distant explosions of supernovae were used to uncover the existence of dark energy and provide a precise numerical account of dark matter. Indeed, time-domain observations of transient events and variable stars, as a technique, influences a broad diversity of pursuits in the entire astronomy endeavor. While, at a fundamental level, the nature of the scientific pursuit remains unchanged, the advent of astronomy as a data-driven discipline presents fundamental challenges to the way in which the scientific process must now be conducted. Digital images (and data cubes) are not only getting larger, there are more of them. On logistical grounds, this taxes storage and transport systems. But it also implies that the intimate connection that astronomers have always enjoyed with their data---from collection to processing to analysis to inference---necessarily must evolve. The pathway to scientific inference is now influenced (if not driven by) modern automation processes, computing, data-mining and machine learning. The emerging reliance on computation and machine learning is a general one, but the time-domain aspect of the data and the objects of interest presents some unique challenges, which we describe and explore in this chapter.