cloud that are different, causing infrared emission from molecules rather than optical emission from atoms and ions. In 2009 the acronym "MHO", for Molecular Hydrogen emission-line Object, was approved for such objects, detected in near infrared, by the International Astronomical Union Working Group on Designations, and has been entered into their on-line Reference Dictionary of Nomenclature of Celestial Objects. The MHO catalog contains over 2000 objects. Ultraviolet Herbig Haro objects HH objects have been observed in the ultraviolet spectrum. See also Protoplanetary disk References External links Catalogue of HH Objects at VizieR Animations of HH object jets from HST observations A Catalogue of Molecular Hydrogen Emission-Line Objects in Outflows from Young Stars: MHO Catalogue Nebulae Star formation Articles containing video clips