NGC 2261: Hubbles Variable Nebula

What causes Hubble's Variable Nebula to vary? The unusual nebula pictured above changes its appearance noticeably in just a few weeks. Discovered over 200 years ago and subsequently cataloged as NGC 2661, the remarkable nebula is named for Edwin Hubble , who studied it earlier this century. Hubble's Variable Nebula is a reflection nebula made of gas and fine dust fanning out from the star R Monocerotis. The faint nebula is about one light-year across and lies about 2500 light-years away towards the constellation of Monocerotis . A leading variability explanation for Hubble's Variable Nebula holds that dense knots of opaque dust pass close to R Mon and cast moving shadows onto the reflecting dust seen in the rest of the nebula.