Welcome to the Exposure Time Calculator (ETC). The ETC is a web-based application developed in python that assists Hubble astronomers and engineers in preparing Phase I and Phase II observing proposals for submission to the Space Telescope Science Institute (STScI). The ETC’s sole purpose is to calculate the following:
Signal-To-Noise (SNR) Ratio (for a given Exposure Time)
Exposure Time (given a desired SNR Ratio)
The ETC calculates SNR or Exposure Time for a simulated astronomical observation using one of Hubble’s primary instruments:
Advanced Camera for Surveys (ACS)
Cosmic Origins Spectrograph (COS)
Space Telescope Imaging Spectrograph (STIS)
Wide Field Camera 3 (WFC3)
Since each instrument on board Hubble is unique with its own image capturing modes, a separate ETC input web page has been created for every combination of instrument and science image modality. A single server shared by all of the instruments, however, handles all the SNR calculations and output pages. This common server uses pysynphot as its synthetic photometry calculating engine.
If you have any questions regarding this calculator, please contact the STScI HST Help Desk. Remember to include your ETC ID.
