A rear sight is provided for use on a firearm. The rear sight includes a rear sight blade connected to a mounting base. The mounting base is configured to be connected to a top surface of the firearm. The blade includes a sighting notch positioned to be aligned with a post on a front sight. The width of the sighting notch is variable. The rear sight is configured to be provided with a second sighting notch integrated within the rear sight and which is configured to move between a first position and a second position.