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4th of March 2022
More Solar System adventures with RACS-high
E. Lenc (CSIRO Space and Astronomy)
Now that ASKAP has completed the first pass of RACS-high observations we have begun to perform a health-check of the data. As with RACS-low, and RACS-mid, this involved checking to see whether any planets happened to wander into the fields as they were being observed (while these can be fun to find they are a bit of distraction when trying to map the sky and can hide more distant background objects). As it turns out, most of the usual suspects were present -- Jupiter (and its polarised radiation belt), Saturn, Uranus, and Neptune. Mercury and Venus were particularly prominent as they no longer appeared as fast moving streaks but were more point-like or, as in the case of Venus, very disk-like -- this is because they were nearing maximum elongation from the Sun as seen from the Earth and so appear as if they slammed on the brakes. Venus was on the same side of the Sun as the Earth and so quite close to us, making it appear much larger than in previous observations. With optical telescopes, under such conditions, Venus would appear as a very thin cresent because the Sun is behind it. The view with a radio telescope is quite different as we don't see the phase of Venus, instead we "see" its heat -- and it is hot all over.

Surprisingly, the only planet to evade detection during RACS-high was Mars - presumably wandering off an unobserved field and into an observed field before ASKAP could catch it. However, there was a new kid on the block during RACS-high. It just so happened that ASKAP was observing a RACS-high field that was relatively close to the Sun on the 20th of January 2022 when a solar flare erupted (as seen by Nasa's Solar Dynamics Observatory). Despite being more than 14 degrees away from where ASKAP was observing, it was still possible to detect and locate the position of the flare on the solar disk using the RACS-high data (the disk of the Sun is shown as an outline in the bottom-right image as the flare outshone the Sun itself in radio at that time).

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