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.