Flux

Illustration of airmass correction procedure, measuring flux of star over a range of zenith angles, and extrapolating to zero airmass (ie above the atmosphere).

Corrected for using a flux standard.

• Measure flux from source of known brightness through identical configuration (except for exposure time).
• Relative counts of source to standard gives the flux calibration.
• For a spectrometer, by opening up the slit can estimate slit losses.
• For photometry determine the air mass correction for each by measuring the flux of a bright star at a range of zenith angles.