
	User's Guide Contents
	Return to ETC Welcome SYNPHOT SNR and Exposure Time SNR Time Optimal SNR Spectroscopy Target Acquisition Basic Use Page Heirarchy Reference Extraction Regions Spectral Distribution User Spectra Other Spectra Extinction Normalization Background CCD Parameters ID Number Calculations SYNPHOT Calls Call Descriptions Call Parameters NICMOS Spectroscopic Extraction Regions Tables Spectral Elements NICMOS Filters NICMOS Dispersers ACS Filters and Dispersers COS Dispersers WFC3 Filters and Dispersers STIS Filters and Dispersers NICMOS Tables COS Tables STIS Tables and Topical Help

Welcome to the Exposure Time Calculator (ETC)

Welcome to the Astronomer Proposal Tool (APT) Exposure Time Calculator. The ETC is a web-based application developed in Java 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)
[future] Cosmic Origions Spectro (COS)
Near Infrared Camera and Multi Object Spectrometer (NICMOS)
Space Telescope Imaging Spectrograph (STIS)
[future] Wide Field Camera 3 (WFC3)

Since each instrument onboard Hubble is unique with its own image capturing modes, a separate ETC input web page must be 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.