Although Forex is active 24/7, not every hour is suitable for scalping.
No scalper wants to sit in front of the monitor for numerous hours bored and disappointed with the �sleeping� price as it literally moves nowhere.
Scalpers hunt for volatile, liquid market. There are 4 major market sessions: London, New York, Sydney and Tokyo session. To trade effectively scalper needs to learn behavior of a chosen currency pair and define most active sessions, even particular hours for this pair to be able to catch good price moves.