Learning about Learning and Machine Learning

Learning: the activity or process of gaining knowledge or skill by studying, practicing, being taught, or experiencing something (Merriam-Webster Dictionary)

Machine Learning: Machine Learning is the field of scientific study that concentrates on induction algorithms and on other algorithms that can be said to “learn”. (Ron Kohavi, Stanford)

Machine learning was utilized to classify two subtypes of classical Cepheid variable stars: fundamental mode and first overtone. Stars in nearby galaxies are classified manually, and used as the training set. Both subtypes obey separate period-luminosity relations (an approximately linear relation), where fundamental mode Cepheids are brighter than first overtone (see red and blue points in figure below). When using the training data on a target galaxy, the difference in distance causes a shift in all brightnesses, and thus the target is shifted until it is “well aligned” with the training data according to two likelihood functions. (R. Vilalta, K. Gupta, and L. Macri, 2013)