A qualitative introduction to the basic concepts and ideas

Interferometric astronomy is founded on the basic principles of interference of light waves, which were first conceived in the seventeenth century by Christiaan Huygens, based on experimental evidence by F. M. Grimaldi and Robert Hooke. Interference itself was studied quantitatively in the nineteenth century, beginning with Thomas Young and Augustin Fresnel, and quickly blossomed into the major subject of physical optics. The first application of interference to astronomy was proposed by Hyppolyte Fizeau in the middle of that century.

The purpose of this chapter is to cover the basic ideas of optical interference relevant to astronomy in a qualitative manner. It is followed by two chapters describing the concepts in a more mathematical way. Some of the tools (particularly Fourier analysis), which are essential to detailed understanding of the subject, but may well be quite familiar to many readers, are described in Appendix A.

Young's experiment (1801–3)

This book is about the application of interference to optical astronomy. The possibility of interference is the major distinction between particles and waves as mechanisms for transporting energy and momentum, and the phenomenon of “destructive interference,” in which two disturbances cancel one another out under specific conditions, is peculiar to waves and cannot occur with particles. Although it might seem that energy is somehow being destroyed under these conditions, we always find that the energy which appears to have been lost when two waves interfere destructively appears somewhere else in the system, so that there is, almost miraculously, never any problem with its conservation.