I think people here in

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Dominic Ford

I think people here in Cambridge would say it’s an indication of just how good the Gaia data now is that all these biases can be measured and corrected.

None of these effects were measurable before, because they were entirely hidden in random noise. The measurements are now so stable and repeatable that these systematic skews start becoming apparent.

This is one of the reasons why so much work goes into every Gaia data release, and why successive data releases can’t simply come out at the push of a button. When you get rid of all the random noise, what’s left is the systematic noise, and that’s where the really hard work begins.

I work on the PLATO mission, and we’re seeing similar trends there. We set E2V the challenge of building the lowest-noise CCD they’ve ever made. What happened last year when they got rid of all the random thermal noise? They discovered entirely new leakage current patterns which no mission has ever seen before, because they’d always been entirely hidden in the noise before.