The first Monthly Media for 2020 is from Dr Ben McKinley and undergraduate student Lauren Springer, who bring us a visualisation of FM radio transmissions from Earth that bounce off the Moon and back onto the Murchison Widefield Array (MWA) telescopes.

Some of the radio signals humans use to communicate reach the surface of the Moon that faces towards the Earth, causing it to bounce back down to us, as depicted in the below image. This is a very small effect, but in the search for the extremely faint Epoch of Reionisation (EoR) signal, every piece of noise must be found – and eliminated!

Radio signals from FM radio transmitters around the globe can bounce off the Moon and be reflected back down onto very sensitive radio telescopes, such as the MWA, making it difficult to observe very faint signals from the Universe, such as the EoR signal.

The below GIF shows a simulation of the FM radio signals bouncing off the Moon and back at the MWA. The Moon begins below the horizon for the MWA (the MWA can’t see the Moon), becoming visible between 8 – 22 hours into the simulated observation (or 5 seconds to 14 seconds of the video). The brightness at each frequency (top left panel) becomes very dim around halfway as the Moon is mostly above the Pacific ocean, where there are very few FM radio transmitters.

In the bottom panel you see the Earth, as if you stretched its spherical shape into a flat rectangle, with the yellow dots representing all the FM radio emitters within the frequency range of 88.5 – 108 MHz (FMLIST database). In the video, these dots turn red if the MWA (shown with the pin) and the radio emitter can both see the Moon above their horizons at the same time. In the top right panel you can see the Moon’s position relative to the horizon of the MWA. The top left panel shows the brightness of the reflected FM radio transmission at each frequency off the Moon and onto the MWA.