NGC 2261 is an unusual nebula in that it's appearance can change in a matter of weeks. The most plausible explanation is denser knots of gas closer to the star R Mon at the tip of the nebula cast shadows on the reflecting dust located further out. The star R Mon itself is encased in a think shell of dust. The nebula is named after Edwin Hubble who studied it. The nebula is about 1 light year across and is 2,500 light years away in the constellation of Monoceros. The nebula was discovered by William Hershel in 1783, and was the first object photographed by the 200 inch Hale Telescope at Palomar.
Image of it taken 9 months ago next to a more recent image, you can see variations in the patterns of the nebula.