The Lump Star is the reflection nebula NGC 2023: one of the brightest sources of fluorescent molecular hydrogen in the sky. It is powered by the B star (B1.5) HD 37903, the most luminous member of a cluster of young stellar objects illuminating the front surface of the Lynds 1630 molecular cloud (Barnard 33) in Orion B (see Orion Complex). NGC 2023 forms a cavity in the surface of the cloud, some 450 parsecs from us, producing both a bright visual reflection nebula and a ultraviolet-excited photodissociation region. The Lump Star lies close by the famous Horsehead Nebula in Orion.