This page gives the exposure time and the precision for a photometric observation.
The curves the model uses for this instrument, sky and star.
Python is still loading.
Python is still loading.
Python is still loading.
The sky and the star are in photons, and the detected curves in electrons. Download these curves as CSV, at every 1 nm point from 0.3 to 3 µm.
If you change a value below, the preset becomes Custom.
The ETC multiplies these two curves together. The result is the system response. A new pair takes a moment to build the first time.
Two columns: wavelength, then the fraction of light that passes. The ETC reads nanometres, ångströms or microns, and percent or a fraction, and says which it used. Download a template.
The slider covers 0.01 pc to 1 Mpc. You can also type a value.
Press Enter to load the star. The ETC reads its distance and brightness from Gaia, then scales the model to match.
Gaia's own temperature is ignored while this is ticked.
Leave these empty to let the ETC pick any exposure time.
Python is still loading.
This is an exposure time calculator for ground-based astronomical photometry. You give it a telescope, a camera and a filter. It returns the exposure time that fills the detector well, the precision of one frame, and the precision after you bin the frames over a chosen time.
It also breaks the result into its noise sources: the star itself, scintillation in the atmosphere, the sky background, dark current and read noise. The noise sources add in quadrature. The chart shows which one limits your observation, so you know what to improve.
The model multiplies three curves together: the efficiency of the telescope and its optics, the quantum efficiency of the detector, and the transmission of the filter. The result is the system response. It then integrates that response against a stellar spectrum and against models of sky transmission and sky radiance for Paranal at 2400 m.
Water vapour and airmass set the state of the atmosphere. The effective
temperature and the distance set the star. You can instead give a Gaia
DR3 source_id. The page then reads that star's parallax
and its BP, G and RP fluxes from VizieR, and scales the model to match
the real star.
It suits anyone who plans photometry of stars, transiting exoplanets or other variable sources, and anyone who designs an instrument and wants to know which parameter limits the precision. The stellar parameters come from a modern dwarf star sequence.
The calculator runs the open-source mphot Python package. It runs as WebAssembly in your browser, so no server does the work and nothing you type is sent anywhere. For the method, see Pedersen et al. 2024. The package documentation is at mphot.readthedocs.io.