The Sharpless catalog of emission nebulae contains 313 entries representing H-II emission nebulae with a declination of -27 degrees or above. Compiled and published by American astronomer Stewart Sharpless (USNO) in 1959 (see here), the catalog contains a wide variety of star formation regions across the Milky Way including various Herbig-Haro and Wolf-Rayet objects as well as a number of well-known emission nebulae such as the Trifid (M20), the Eagle (M16), Orion (M42), Lagoon (M8), the Crescent (NGC 6888), and the Crab (M1) nebula.

Note: This impressive and bright emission nebula in Cygnus, more commonly known as the Tulip Nebula, lies very close to η-Cyg (mag 3.89) and spans 8.8 light-years in diameter. Lying at a distance of 8,750 light-years away, the excitation of hydrogen and the consequent nebula emission is attributed to the O6.5III class star HD 227018 (mag 9.02) (see the bluish star in the lower half of the nebula below and lying to the immediate upper right of the bright orange star SAO 69230 (mag 7.69)). What is of great interest is the fact that the well-known black hole candidate Cygnus X-1 lies very close to the Tulip Nebula and which is just outside the field of view at the bottom right corner. Sh2-101 is ideally placed during summer and early fall where it is directly overhead immediately after darkness.