R Monocerotis, abbreviated R Mon, is a very young binary star system in the equatorial constellation of Monoceros. The apparent magnitude of R Mon varies between 10 and 12 and the spectral type is B8IIIe. This is a massive Herbig Ae/Be star, a type of pre-main-sequence star that is surrounded by an orbiting circumstellar disk of gas and dust. This disk has a mass of ~0.007 Solar mass and extends outward to a distance of under 150 AU from the host. Because of this dust, the star is obscured from direct visual sight but can still be observed in the infrared. R Mon is still in the accretion phase of star formation and it is driving an optically opaque bipolar outflow with a velocity of 9 km/s. The northern flow is blue-shifted, and thus moving more toward the Sun. There is a T Tauri-type stellar companion at an angular separation of 0.69 arcsecond from the primary. This system is located in a diffuse nebula called "Hubble's Variable Nebula" (NGC 2261), which is being illuminated by a conical beam of light from the primary.