annuluses

Annulus refers to a ring-shaped object or space. In geometry, an annulus is the region between two concentric circles. It is often described as a ring or a washer shape. The area of an annulus can be calculated by subtracting the area of the inner circle from the area of the outer circle.

In astronomy, an annulus is a ring of diffuse material or a collection of objects orbiting a celestial body in a ring formation. Saturn's rings are a famous example of an annulus in space, composed of countless particles of ice and rock. The term can also describe the ring-like structures found in nebulae.

In biology, an annulus can refer to a ring-shaped structure or marking. For example, the annual growth rings in trees can be considered an annulus, indicating a year of growth. Some biological structures, such as the ciliary annulus in the eye, are also described as annular.

In mechanical engineering, an annulus is the space between two concentric cylinders or pipes. This annular space is often used for fluid flow or heat transfer. For instance, the space between a pipe and its casing creates an annulus. The term is also used to describe sealing rings or gaskets that fit into annular grooves.