A mariner's guide is a navigational tool used by sailors to help them find their way on the open seas. The term can refer to a variety of different tools, such as a POLESTAR, STAR, POLARIS, and LANDMARK. A POLESTAR is a STAR that is used for navigation, usually the North STAR. A STAR is a celestial body that emits light and is visible in the night sky. POLARIS, also known as the North STAR, is the brightest STAR in the constellation Ursa Minor. A LANDMARK is an object or feature of a landscape that is easily recognizable and can be used to orient oneself. All of these tools are used together to create a mariner's guide, which helps sailors find their way on the open seas.