Herbig-Haro objects near NGC 2023

Where the dark outline of the famous Horsehead nebula dissolves into the Lynds 1630 molecular cloud is the striking reflection nebula NGC 2023, seen as the blue blob on our well known colour photograph.

On the red plate of the three-colour series used to make the colour image, several small, elongated red nebulae were found (arrowed here). Spectra showed them to be Herbig-Haro objects, often the first visible signs of otherwise hidden star formation. The implications of this discovery are discussed in a paper by Ogura, Walsh and Malin where this illustration appears.

The NGC 2023 reflection nebula holds other surprises, as described in the paper by Witt and Malin
Original plate taken with the Anglo-Australian Telescope