CTIO Exposure Calculator Help

Wavelength

Enter wavelength of interest in Ångstroms. This is the wavelength at which the flux or magnitude is specified and the S/N calculation is performed.

Select Lunar Phase

Dark = ±0d; Grey ±7d; Bright ±14d.

Airmass

Mean airmass averaged over the observation.

Johnson magnitude

The magnitude of the object in the band (UBVRI) that contains the wavelength of interest. The use of broadband magnitudes will give a less accurate result for extremely red or blue objects, objects with non-stellar continua and emission line objects than using monochromatic magnitudes or fluxes.

AB

Monochromatic magnitude defined as 
 
AB = -2.5 log(F_lambda) - 5 log(lambda) - 2.40 

  with F_lambda in ergs/cmº/s/Å.
         lambda in Ångstroms
  
          -- or -- 

AB = -2.5 log(F_nu) - 48.60 

  with F_nu in ergs/cmº/s/Hz.

F_lambda

Monochromatic flux with units of ergs/cmº/s/Å.

F_nu

Monochromatic flux with units of ergs/cmº/s/Hz.

Max Exposure Time

Split total exposure time into largest equal increments not exceeding this Maximum Exposure Time. You are trading off cosmic rays vs. readout noise.

Total Exposure Time

Total combined exposure time in seconds for all exposures. Required if you are calculating the S/N for a given exposure time.

Desired S/N

Enter desired Signal/noise ratio at given wavelength (PER PIXEL). Required if you are calculating the exposure time to reach a given S/N.

Calculate S/N for specified Total Exposure Time

Select either this button or the one below it.

Calculate Total Exposure Time to reach Desired S/N

Select either this button or the one above it.
Michael Keane (mkeane@noao.edu)