An online telescope is an astronomy tool that usually takes one of two forms. In the first, previously made observations are collected into a database that is accessible online. In the second, physical telescopes are made available for observations by request or are directly controlled by users online. The collation of existing data and images is generally referred to as a virtual telescope or observatory. Online interface with a physical telescope is often referred to as an Internet telescope.
The International Virtual Observatory Alliance (IVOA) is composed of 19 member observatories worldwide. The objective of the organization and its members is to collect and collate existing data, put it into a standardized format and make it available for online research. Decades of astronomical observations with various devices at multiple wavelengths are brought together for data mining. This information is stored in a central database that can be accessed over the Internet.
In a less research-oriented format, services such as Microsoft® WorldWide Telescope offers a planetarium type of online telescope. Tours of astronomical bodies are offered as is in-depth instruction making use of high-resolution photography. Such services typically provide an interface allowing users significant freedom in their explorations. The night sky from any point on earth at any time in the past or future can be recreated. The virtual space traveler can select his or her own itinerary to visit the objects of most interest.
A more hands-on online telescope is offered by services that make live observations from home a reality. One online telescope offers access to a predetermined schedule of observations made by telescopes in various countries. The images are transmitted in real time and are accessible to any with Internet connectivity.
The selection of what to observe and direct control of a remote telescope is also made available over the Internet. This is for the more advanced observer and requires some degree of technical training before the controls are turned over to the user. This service is usually fee-based unless one is affiliated with the observatory or university that owns the telescope.
As a compromise, the serious amateur might consider those observatories that accept requests for specific observations. On-site staff retains direct control of the telescope while fulfilling the observational requests of third parties. The photographic results and pertinent data, such as atmospheric conditions, are forwarded to the end user, often digitally in real time. This is, in fact, the normal procedure involving the use of highly advanced systems. The professional astronomer relies on a dedicated support staff experienced in the use of the device.