If you visit the senate chamber during a session on an average day, you're most likely to find the session presided over by

Although the Constitution states that the Vice President is vested with the power to preside over the Senate, the Vice President is often not in attendance. Instead the "pro tempore" presides over the Senate when the Vice President is not present and typically those presiding over the Senate are junior Senators. 

Its a and i dont acually know