Transcript: Astronomers have used deep multi-wavelength observations of the sky to try and determine the history of star formation in the universe. That is the sum of the formation processes of all stars in all galaxies over cosmic time. This ambitious task is important in terms of deciding how the history of galaxies occurred. It’s a difficult procedure because measurements of the blue light of nearby galaxies correspond to something entirely different at high redshift. For example the blue light observation of a nearby galaxy corresponds to relatively young stars, but by high redshift that blue pass band is selecting far ultraviolet light which can correspond to very short-lived times of star formation. Thus a fixed filter pass band selects entirely different types of stellar populations at high and low redshift which is why astronomers must combine multi-wavelength observations in the optical and infrared spectral regions. In addition, dust can obscure galaxies, and in particular young galaxies are expected to be dust-enshrouded. Visible light cannot penetrate dust so infrared observations are needed to study high redshift galaxies.