A moonsail, also known as a moonraker, hope-in-heaven, or hopesail, is a sail flown immediately above the skysail (see sail-plan) on the very top of the royal mast on large, square rigged sailing ships of the clipper era. None of the four and five masted square-rigged ships carried a moonsail.

This is a relatively unusual sail only used on ships built primarily for speed.