NGC 2023

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The reflection nebula NGC 2023 is in the constellation Orion. It is one of the brightest sources of fluorescent molecular hydrogen with 4 light-years of largest 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.

NGC 2023 forms a cavity in the surface of the cloud, some 450 parsecs from Earth. It produces a bright visual reflection nebula and a ultraviolet-excited photodissociation region. It is about a third of a degree from the Horsehead Nebula and is often included (but not indicated) in images of that object.