Low Frequency Radio Astronomy from the Ends of the Earth
Redshifted 21cm emission from neutral hydrogen is rapidly becoming one of our most powerful observables in cosmology. With it, we can study the evolution of dark energy at low/intermediate redshifts, the epoch of reionization, the first stars in the universe during cosmic dawn, and hopefully one day the cosmic dark ages. Unfortunately at higher redshifts, human-generated interference is a major barrier to 21cm studies (see: https://xkcd.com/2226/). To avoid this interference, we have set up radio telescopes in some of the most remote places on Earth, from the Canadian high Arctic to the sub-Antarctic. I will review the physics of the high-redshift 21cm emission history, discuss the current state of cosmic dawn measurements, and describe some of our current efforts to probe cosfic dawn, and to begin opening a window on the very low-frequency (<10 MHz) sky, which is currently almost completely unexplored.