Solar System Objects
The Rapid ASKAP Continuum Survey (RACS) can be used to search for radio sources that vary over time-scales of minutes, days, months or even years. Since the survey can be repeated on relatively short time-scales compared to historical surveys it can also detected sources that notably change position over these time-scale. While completing the first epoch of RACS we ended up following in the paths of the ancients and re-discovered a couple of local favourites which are compiled in the images below. Planets, the name itself derived from an ancient Greek word meaning “wanderers”, move across the sky and so can appear as transients.
Mercury lives in the fast lane and would normally be blurred over the course of a 15 minute RACS observation but when tracked we have just enough sensitivity to detect this tiny planet.
Venus is a fast mover but also bright – in this instance we see the trail as it moves relative to the background sky in just 15 minutes.
The Moon, also a fast mover, is big, bright, and rather annoyingly masks out background sources. In contrast, the outer planets take a more leisurely approach to their wanderings and appear as transients over periods of months.
When we look at Jupiter at radio wavelengths what we actually see are its radiation belts – these appear as emission on either side of the planet.
Saturn appears as a simple dot because, unlike in optical, radio doesn’t see the ring.
Mars was on the other side of the Solar System when it was observed with RACS and is only just barely detectable as a slightly blurred object.
Uranus and Neptune, while they were within the field of view of a number of RACS observations, were too weak to be detected.