We present early results from a project to measure the sky-averaged (global), redshifted $21,$cm signal from the Epoch of Reionisation (EoR), using the Murchison Widefield Array (MWA) telescope. Because interferometers are not sensitive to a spatially-invariant global average, they cannot be used to detect this signal using standard techniques. However, lunar occultation of the radio sky imprints a spatial structure on the global signal, allowing us to measure the average brightness temperature of the patch of sky immediately surrounding the Moon. In this paper we present one night of Moon observations with the MWA between 72 - 230 MHz and verify our techniques to extract the background sky temperature from measurements of the Moons flux density. We improve upon previous work using the lunar occultation technique by using a more sophisticated model for reflected `earthshine and by employing image differencing to remove imaging artefacts. We leave the Moons (constant) radio brightness temperature as a free parameter in our fit to the data and as a result, measure $T_{rm{moon}} = 180 pm 12 $ K and a Galactic synchrotron spectral index of $-2.64pm0.14$, at the position of the Moon. Finally, we evaluate the prospects of the lunar occultation technique for a global EoR detection and map out a way forward for future work with the MWA.
Download