virtual telescope, a computerized interferometer (see interference) that merges the images from two or more telescopes to obtain a single, large, enhanced image. The image in each telescope is made from electromagnetic waves (light waves from an optical telescope, radio waves from a radio telescope), each wave having peaks and valleys. Combining several waves into one makes the peaks higher and the valleys lower, resulting in a single, enhanced wave. This tends to make stars appear to be brighter and to increase the distances at which celestial objects can be studied. The peaks and valleys can also be made to cancel each other out (in a process called nulling interferometry) to permit the selective diminishment of the brightness of the light from a star so that, for example, a dimmer star or planet can be studied.

virtual reality (VR) or virtual environment (VE), computer-generated environment with and within which people can interact. The advantage of VR is that it can immerse people in an environment that would normally be unavailable due to cost, safety, or perception restrictions. A successful VR environment offers users immersion, navigation, and manipulation. VR encompasses a range of interactive computer environments, from text-oriented on-line forums and multiplayer games to complex simulations that combine audio; video, animation, or three-dimensional graphics; and scent. Some of the more realistic effects are achieved using a helmetlike apparatus with tiny computer screens, one in front of each eye and each giving a slightly different view so as to mimic stereoscopic vision. Sensors attached to the participant (e.g., gloves, bodysuit, footwear) pass on his or her movements to the computer, which changes the graphics accordingly to give the participant the feeling of movement through the scene. Computer-generated physical feedback adds a "feel" to the visual illusion, and computer-controlled sounds and odors reinforce the virtual environment. Other VR systems, such as flight simulators, use larger displays and enclosed environments to create an illusion. Less-complicated systems for personal computers manipulate an image of three-dimensional space on a computer screen. In a virtual network many users can be immersed in the same simulation, each perceiving it from a personal point of view. VR is used in some electronic games, in amusement-park attractions, in military exercises, and to simulate construction designs. Experimental and envisioned uses include education, industrial design, surgical training, and art.

virtual observatory, a collection of integrated astronomical data archives and software tools that utilize computer networks to create an environment in which research can be conducted. Several countries have initiated national virtual observatory programs that will combine existing databases from ground-based and orbiting observatories and make them easily accessible to researchers. As a result, data from all the world's major observatories will be available to all users and to the public. This is significant not only because of the immense volume of astronomical data but also because the data on stars and galaxies has been compiled from observations in a variety of wavelengths—optical, radio, infrared, gamma ray, X-ray and more. Each wavelength can provide different information about a celestial event or object, but also requires a special expertise to interpret. In a virtual observatory environment, all of this data is integrated so that it can be synthesized and used in a given study.

Use of computer modeling and simulation to enable a person to interact with an artificial three-dimensional visual or other sensory environment. A computer-generated environment simulates reality by means of interactive devices that send and receive information and are worn as goggles, headsets, gloves, or body suits. The illusion of being in the created environment (telepresence) is accomplished by motion sensors that pick up the user's movements and adjust his or her view accordingly, usually in real time. The basis of the technology emerged in the 1960s in simulators that taught how to fly planes, drive tanks, shoot artillery, and generally perform in combat. It came of commercial age in the 1980s and is now used in games, exhibits, and aerospace simulators. It has potential for use in many fields, including entertainment, medicine and biotechnology, engineering, design, and marketing.

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