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The image above may, for some, invoke memories of spirograph
patterns from their childhood.
Spirographs used toothed wheels within wheels to generate curved patterns technically known as hypotrochoids and epitrochoids.
In fact, the figure above shows a portion of the sky coverage achieved by the
Parkes S-Band Polarization All Sky Survey (S-PASS), conducted at 2.3 GHz.
The survey used long scans in azimuth to map out long tracks as the sky rotated.
A complete description of the survey and maps produced is
given
in the preprint of the paper by Carretti et al.,
to be published in
Monthly Notices of the Royal Astronomical Society.
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