The Lagoon Nebula (catalogued as Messier 8 or M8, NGC 6523, Sharpless 25, RCW 146, and Gum 72) is a giant interstellar cloud in the constellation Sagittarius.

In the sky of Earth, it spans 90' by 40', which translates to an actual dimension of 110 by 50 light years.

The nebula contains a number of Bok globules (dark, collapsing clouds of protostellar material), the most prominent of which have been catalogued by E. E. Barnard as B88, B89 and B296.

It also includes a funnel-like or tornado-like structure caused by a hot O-type star that emanates ultraviolet light, heating and ionizing gases on the surface of the nebula.

In 2006, four Herbig–Haro objects were detected within the Hourglass, providing direct evidence of active star formation by accretion within it.