weird bright z-sky for expids=273526-29 on 20250114 (tileids 26893 and 22176)

[araichoor]

I cannot figure out what happens, but something happened for expids=273526-30 273526-29 on 20250114 (tileids 26893 and 22176)!
I ll mark those as "unsure".
the sky became brighter (0.3 mag) in the red for those exposures, and this affects the redshifts.

here are the spectro. sky brightnesses:

those exposures were close to the moonsep=45 limit, but also do later ones, so one cannot blame the moon I think (which, moreover, is "blue"):

nothing particular in the spacewatch movie.
there is a small comment in the nightlog for 273526:

00:40 [07:40] Exp. 273526- Not Sure - Mostly good. Seeing 1.0", transparency 98%. One quadrant of z1 CCD is completely masked out, and one quadrant of r1 CCD his higher rate of cosmic ray masking. (SO)
Tile 26893, Exptime: 1452.79, Airmass: 1.46, Sequence: DESI, Flavor: science, Program: BRIGHT

here are the tileqa plots (note the alert messages, the redshifts at z=1.6, and the low amplitude n(z)):

and here is one sframesky plot:

[schlafly]

I think when we have seen this in the past we have said something like "there must be some weird scattered light path that leads to havoc at very particular angles" and then marked these as bad. If that's right, then the redness is a statement about the reflectivity of some surface?

[araichoor]

thanks, I didn t remember that!
@abhi0395: based on Eddie s comment, let s mark those 273526-29 exposures as bad, thanks!

(ps: I ve edited the issue title and initial message, as I wrongly included 273530 then).

[geordie666]

@rongpu: can you mark these exposures as bad this week, please?

[rongpu]

I have marked exposures 273526-273529 as bad.

[schlafly]

I think the workflow needs to be:

• exposures get marked as bad and reprocessed
• someone clears QA
  I think these exposures have not yet been reprocessed? At least, this still looks ugly. https://data.desi.lbl.gov/desi/spectro/redux/daily/tiles/cumulative/22176/20250114/tile-qa-22176-thru20250114.png