Cone nebula, optical image. This nebula lies in the southern region of the Christmas Tree cluster NGC 2264. The reason for its shape is unknown, although the region seems to consist of clouds of dust and gas which obscure the light from the emission nebula and open cluster of stars behind. One theory is that there is a strong wind blowing past the apex of the cone, which is a Bok Globule or cloud of gas condensing to form a star. The Cone nebula is 7 light years in length, and lies 2700 light years from Earth in the constellation Monoceros.