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13th of June 2017
The MWA's View of the Moon against the Milky Way
by Natasha Hurley-Walker (Curtin University)
This observation was taken as part of the GaLactic and Extragalactic All-sky Murchison Widefield Array (GLEAM) survey (Wayth et al. 2015), and recently reprocessed with an improved pipeline aimed at releasing the Galactic part of the survey to complement the existing extragalactic catalogue (Hurley-Walker et. al 2017). Spanning 72 to 231 MHz, the survey explores the sky at low frequencies, and visible in this image are bubble-like supernova remnants, extended HII regions, background radio galaxies, as well as the diffuse synchrotron emission of the Milky Way itself. This image was constructed using just five minutes of observing, 50% of the field-of-view, and 60% of the bandwidth, which has been split into three "radio colours": red = 72 - 103 MHz, green = 103 - 134 MHz, and blue = 139 - 170 MHz. By happy accident, our Moon is silhouetted against the background glow of the Milky Way. The red dot in the centre shows the reflection of the Earth's FM radio transmissions from the tangent plane of the face of the Moon; the rest appears black because as a blackbody, the Moon is much dimmer than the Milky Way's bright synchrotron emission. McKinley et al. 2013 used the Moon's FM reflection to determine how bright the Earth might appear at meter wavelengths to an observer beyond our own solar system.

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