McKay et al. present a precision measurement of radio sky brightness over 60–350 MHz. Accurate knowledge of the radio sky over these frequencies is essential for modelling foregrounds in experiments targeting cosmic dawn and the epoch of reionization. Measurements below 1 GHz are also needed to understand the Galactic cosmic ray electron spectrum, constrain nanojansky radio source populations and dark matter models, understand origins of the diffuse radio background, and improve calibration of long-wavelength radio telescopes. McKay et al. show that current all-sky maps and the 2016 Global Sky Model (GSM2016) require substantial corrections over 60–350 MHz. This significantly increases previously inferred excess radio background, motivating review of faint source populations and dark-matter decay models. The measurement used a new receiver architecture that self-calibrates its noise contribution and bandpass in situ while connected to an antenna. Sky models scaled to these measurements can set the absolute flux-density scale for SKA-Low and other low-frequency radio telescopes.

The image above shows the observing system at Inyarrimanha Ilgari Bundara, the CSIRO Murchison Radio-astronomy Observatory.  A single, accurately modelled, log-periodic SKALA4.1 antenna at the centre of a 40 m diameter SKA-Low station ground mesh is connected via a 3.1 m coaxial cable to the smaller GINAN receiver box at the base of the antenna that contains an RF switch, calibration loads, and a noise source. The smaller box is connected via a 19 m coaxial cable to the main GINAN receiver box in a tent at the edge of the mesh.  GINAN is a collaboration to make radio measurements of Global Imprints from Nascent Atoms to Now.  Ginan is the name the Wardaman people of northern Australia give to the fifth brightest star of the Southern Cross which they saw as “a small dilly bag full of knowledge, songs of knowledge that were passed on.”