SQL Server 2008 R2 Readable Mirror
A SQL Server 2008 R2 mirror is not itself readable.  

If you are using Enterprise Edition, you can create a named snapshot database from the mirror.  This allows you to create a point-in-time readable database that can be used for pretty much any query that does not do any updates.  (Though you could use another database (tempdb or a workdb) to do auxiliary work that would not fit the read-only snapshot.)

See: https://msdn.microsoft.com/en-us/library/ms175158(v=sql.105).aspx

When the snapshot gets 'old' enough you create a new snapshot database. You will eventually need to drop the older snapshot, but it is possible to support several snapshots. (This depends on the amount of activity in your database and server.)

If you use Standard Edition and have the same need, look into log shipping using RESTORE with STANDBY.  You will need to manage when the next restores get made in order to use the STANDBY feature. 

See: https://msdn.microsoft.com/en-us/library/ms178615.aspx

It says of the STANDBY option: "The standby file allows a database to be brought up for read-only access between transaction log restores and can be used with either warm standby server situations or special recovery situations in which it is useful to inspect the database between log restores."

Therefore, this method requires you to delay the restore of logs to match the schedule for how long you want to keep this point-in-time in action.  A LOG Restore will end the STANDBY and restore to the following point, which could be restored with a new STANDBY period.

Depending on your needs one of these approaches can give you a readable point-in-time  database. No updates become visible in the database for the period of (a) the snapshot, or (b) the period between restoring updates.