Modern astrophysics requires the use of observations over the broadest range of wavelengths to fully understand the physical nature of the objects and processes we wish to study in the universe.

Data are obtained from ground-based and space-based observations operating in radio, infrared, visible, ultraviolet, x-rays and gamma rays. The design and operation of the instrumentation used to gather this information, the telescopes and detectors themselves, depend on the interaction between matter and radioactivity at the different wavelengths and requires in-depth knowledge of the findings of molecular, atomic, nuclear, and particle physics.

The observer needs to have the data at hand to understand the properties and the limitations of the instrumentation and their relevance to data reduction, analysis, and interpretation.

The theorist who is seeking new models to interpret the findings from the most sensitive and sophisticated observatories that ever existed needs, from time to time, a reality check with what is known.

The Handbook of Space Astronomy and Astrophysics gathers in one place the most frequently-used information in modern astrophysics and presents it in the most useful fashion to the non-specialist in a particular field.

I always loved the chapter on relativistic astrophysics and I am glad it has been retained and improved. I am also glad for the new chapters on experimental subjects that bring the Handbook up-to-date.

I am certain that some young person will find here, as I did, useful food for thought and inspiration that he or she will need to design the next generation of telescopes.