Astronomy Colloquium

As part of the conference "Celebrating the Legacy of the Spitzer Space Telescope", I will highlight the progress made in studies of high redshift galaxies using a remarkable 85cm aperture telescope. This will be a personal selection of topics describing achievements made in our understanding of the assembly history of galaxies, the growth of the quiescent population, and the role of nebular emission in diagnosing early star formation. I will conclude with a largely unforeseen aspect of Spitzer science - determining the demographics of the most distant known galaxies deep into the era of cosmic reionization, which has provided a first indirect glimpse of "cosmic dawn". Spitzer has truly laid the foundation for the next steps in exploring the early universe now eagerly anticipated with the James Webb Space Telescope.