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I think you need to quantify what you mean by "most professional". Some of the more expensive apps are capable of sending coordinate data to position a telescope. This feature is probably very useful to amature astronomers who have access to the required equipment but would be overkill for stargazing. I have Distant Suns 3, which is @ $10 and the NASA app which is free, both of which I'd recommend for stargazing with the unaided eye