AbstractRecent seeing measurements at the Anglo-Australian Telescope (AAT) point towards the thermal characteristics of the telescope itself, in particular the temperature difference between the mirror and the dome air, as the most important factor degrading the seeing, more so than the temperature difference between the inside and outside air. We present the findings, propose clarifying experiments, and discuss possible remedies. We set the realistic target for the AAT to achieve median seeing of 1·5″ rather than the current 1·8″.