What’s a bakeout?
Seeing CCD BAKEOUT on your favorite SOHO images?

From NASA website:
What’s a CCD bakeout, anyway?
In order to (i) keep read noise down (suppress the “snow”) and (ii) prevent cosmic ray hits from permanently raising the read noise level by damaging the detector, the EIT CCD is usually operated at a temperature of about -67 C. This temperature is achieved by passive cooling: the CCD chip is thermally contacted to a titanium “cold finger” (at far left in the image above) that is attached to a radiator plate that is pointed at a piece of sky perpendicular to the earth-Sun line. Read more…
