Environmental challenges in Astronomy

The detection of faint astronomical signals is limited by natural environmental factors and by artificially generated nuisances, such as radio interference and light pollution. The interference can be mitigated by choosing to locate observatories at places where the natural interference is minimised, and by controlling the nuisance emissions. This article describes the range of the nuisances for astronomy, the scope of the solutions that are available to astronomers and the social organisations that have been used to control them. It also describes the environmental contaminations made by the practice of astronomy itself, including biological contamination of the other planets, and the steps that have been taken to reduce them 1. The Detection of an Astronomical Signal and the Environment As astronomical signal from an astronomical source, such as a star or galaxy, depends on • The spectral distribution of radiated flux from the source F(λ; t). In general, the source will vary in time on some time scale, and possibly periodically. • The distribution of the flux from the source on the sky. Even if the source is so distant that it is effectively a point source, in general the flux from the source will be distributed over a solid angle by natural or instrumental effects. Astronomers attempt to measure the flux from the source over some spectral resolution in order to infer astronomical information about it. Even if the measurement is simply a detection of the source and confirmation of its existence (as in looking at it), the detection is effectively a measurement of the flux of the source by showing that it is above a detection threshold. The source may be attenuated by absorption and detected against a background noise. The background noise may have a spatial distribution and time variability, as well as a spectral distribution of its own. The larger the background noise, the less is the contrast between the astronomical source and the background and the less detectable the astronomical source. The detection and measurement of an astronomical signal is unalterably restricted by the properties of the astronomical source. A distant galaxy is far away, the inverse square law of distance diminishes its flux, and there is nothing that can be done about this! Faint galaxies are in general not only more distant, they are also at the same time viewed as they were long ago and therefore represent the composition of the early universe. …