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Usually observational astronomy is considered to occur on Earth's surface ( or beneath it in neutrino astronomy ).
The idea of limiting observation to Earth includes orbiting the Earth.
As soon as the observer leaves the cozy confines of Earth, the observer becomes a deep space explorer.
Except for Explorer 1 and Explorer 3 and the earlier satellites in the series, usually if a probe is going to be a deep space explorer it leaves the Earth or an orbit around the Earth.

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