A place where stars, planets and other celestial bodies are observed, usually through a telescope; also place for observing meteorological or other natural phenomena.
A lookout (vantage point with a view of the surrounding area)
Systematic observation of places and people by visual, aural, electronic, photographic or other means.
Continuous monitoring of disease occurrence for example.
Close observation of an individual or group; person or persons under suspicion.
In criminal law, an investigation process by which police gather evidence about crimes, or suspected crime, through continued observation of persons or places.