Perhaps you should try some spelling variations:
practical astronomy » nautical astronomy, optical astronomy
astronomy sergey » astronomy survey, astronomy surveys, astronomy seven
pure positional » aware positional, pure conditional, pure rotational
patrick some » patrick home, patrick sole, trick some
patrick pure » patrick burke, patrick part, patrick burk

You may be able to get more results by adjusting your search query.

• If you are trying to use Boolean operators, they must be ALL CAPS: (( the patrick some practical astronomy sergey ) OR ( the patrick pure positional astronomy sergey )).
• Adding a wildcard symbol may retrieve word variants: (( the patrick some practical astronomy sergey ) or ( the patrick pure positional astronomy sergey ))*.