In this chapter we describe the major new observational facilities Canadian astronomers will need in order to attack the astrophysical questions about the universe posed in Chapter 2. These tools must cover all wavelengths from radio through to the ultra-violet, and will combine space-based instruments with ground-based ones. They will be designed and operated in such a way that astronomers in many different sub-disciplines will be able to do observations with them. Many of the technological challenges inherent in constructing these observatories will also present many new and exciting prospects for Canadian industry and technology.

First we discuss "World Observatories". These are the new observatories that will be constructed in the next two decades, on a scale which no single country or small group of countries could afford by themselves, and which will not be duplicated by other consortia. These world observatories will truly be one of a kind and are expected to have a revolutionary effect on our understanding of the universe. They come with correspondingly large price tags: their capital costs are expected to be in the range $500M - $1B US. Investments at these levels will be shared among many nations with the goal of constructing uniquely powerful telescopes which will define the limits of our knowledge for the next decade and even beyond. We divide the world observatories into first generation ones that are expected to become operational in the period 2001-2010, and second generation ones that may be commissioned in 2011-2020.

To place the power of these facilities in context, we show the sensitivities of several of them as a function of wavelength in the accompanying graph. The frequency range along the horizontal axis runs from the radio region on the left hand side, through the sub-mm range, into the infrared and on up to the optical and ultraviolet at the right hand end. The vertical axis indicates the flux (energy intensity) emitted by an astronomical object such as a distant galaxy. The lines in the plot show the smallest flux an object can emit and still be detected by a given telescope. Thus the lower lines are the ones from the most powerful facilities. For example, we see that NGST