Simulating the behaviour and performance of instrumentation is required, in different
forms, at several different times during the development of an astronomical research
project, from preliminary studies of an instrument to the planning of its observations
to the assessment of their quality.
This is a compilation of mostly trivial and boring but (hopefully!?) useful stuff
related to the simulation of astronomical instrumentation behaviour and performance.
In Section 1 some basic optical concepts are reviewed.
Section 2 discusses energies involved in light propagation, its breaking
down in photons and blackbody emission.
In Section 3 reviews some typical representations of the spectrum of
astronomical objects.
Sections 4 and 5 discuss sources of instrumental and sky
background, respectively.
Section 6 reports a few formulae which can be used to compute the SNR to be expected from an observation.
In Appendices A and B, the units of measure
used for angular and photometric quantities, the adopted conventions about
their abbreviations, some useful conversion factors and formulae are given.
Appendix D lists further useful astrophysical constants and conversion factors.
Léna et al. (1998), Schlessinger (1995), and Vaccari (2000) are good
starting points for the adoption of a consistent set of units of measures,
names and symbols.
SI units are generally used throughout the document. Approximate
numerical values of constants (generally given with 4 significant
figures) and analytical relations are indicated by the 
symbol,
whereas the 
symbol is used to indicate exact ("by definition")
relations and physical constants.
