"It is known whether 1st-year photometric accuracy will be enhanced by targeting standards fields in the middle of nights in addition to evening/morning twilight standards. "


  • Zeropoints and extinction coefficients calculated for all standards-field exposures during SV
  • RASICAM data in hand.


  • Compare middle-of-night zeropoints and extinctions coefficients to mean of morning/evening twilights.
  • Calculate RMS deviation of midnight to twilight zeropoints, evaluate statistical significance.
  • For cases where midnight standards differ from the twilights signfiicantly: what conditions indicated by RASICAM?
  • Use night of hourly standards to determine whether midnight standards improved ability to interpolate proper zeropoint to hourly standards.


  • If there is no detectable difference between midnight and twilight photometric solutions, except in cases where RASICAM indicates non-photometric conditions, then midnight standards are superfluous.
  • If midnight standards differ from twilights, but hourly variations are seen to be equally large, then midnight standards are superfluous since they cannot track the night's photometric variations anyway.


  • Absence of photometric variation between twilights means that DES observations need to explicit nighttime standards.
  • Fast photometric variations will have impact on ubercal algorithms' assumptions.
  • Useful midnight standards should be incorporated into OBSTAC algorithm, that some field with standards gets observed near middle of photometric nights.