See if you can make out the different in the following sentences:
Did you see the comets last night?
* have you seen Robert by any chance today? (You are just walking in your company and a colleague of yours ask you whereabouts of Robert.)
* Have you seen the new episode of ' The Walking Dead', It was aired yesterday on amc.
* Did you pass your exam?
* Have you finished your exams?
Put it simply, 'have' implies a sort of connection with the present time while past simple lies in the past with no connection to the present. If you did not managed to see the comets then you will not be able to see them anymore because this action was ended in the past, however, the new episode of walking dead is still downloadable or there is a repeat for that on TV. So in the latter example, you are expected to experience the action sometime around in the future.