To keep track of my images I have split them into the four categories:
Nebulae and Star Clusters are objects associated with our own galaxy, the Milky Way:
Nebulae are interstellar clouds of dust, hydrogen, helium and other ionized gases. There are four types of nebulae:
Diffuse nebulae, which can be Emission Nebulae or Reflection Nebulae
Star Clusters contains Open Clusters, most of them can be found in the spiral arms of our Milky Way, and Globular Clusters, which can be found in a Halo around our galaxy.
Galaxies are objects like our Galaxy, the Milky Way, gravitationally bound systems of stars, stellar remnants, interstellar gas and dust, and dark matter. Almost all of them are many millions of light-years away from Earth. The nearest major galaxy to our Milky Way is the Andromeda Galaxy (Messier 31), approximately 2.56 light-years.
All of the brighter Deep Sky Objects has been catalogued in different catalogues by different astronomers.
For example M 42, the Orion Nebula, is also known as NGC 1976 and LBN 974.
The most important for amateur astronomers are:
M (Messier): A list of 110 nebulae and star clusters by Charles Messier (1730 - 1817). He was a French astronomer and comet hunter and published his catalogue to distinguish between comets and permanent objects in the sky. Because of his equipment at that time he could not distinguish between nebulae and galaxies.
NGC (New General Catalogue): published by John Louis Emil Dreyer in 1888, an attempt to compile a comprehensive list of all deep sky objects known at that time. Most objects has been discovered visually.
IC (Index Catalogue): Index Catalogue and Second Index Catalogue by John Louis Emil Dreyer, between 1888 and 1907, are corrections and supplements to the NGC (New General Catalogue)
vdB (van den Bergh): A comprehensive catalog of galactic reflection nebulae by Sidney van den Bergh in 1966.
Sh2 (Sharpless): A list of 313 HII regions (emission nebulae). The first edition was publishing 1953 with 142 objects (Sh1). The second and final version was published by US astronomer Stewart Sharpless in 1959 with 312 objects. Sharpless also includes some planetary nebulae and supernova remnants, in addition to HII regions.
DWB (Dickel, Wendker, Bieritz): A list of optically visible HII regions by H.R. Dickel, H.J. Wendker, J.H. Bieritz, 1969
LBN (Lynds Catalogue of Bright Nebulae): compiled by Beverly Lynds in 1965. Contains both emission and reflection nebulae.
LDN (Lynds Catalogue of Dark Nebulae): A comprehensive catalog of galactic dark nebulae by Beverly Lynds in 1962.
PGC (Principal Galaxies Catalogue): G. Paturel, P. Fouque, L. Botinelli and L. Gougenheim, 1989 and 1995
For best viewing adjust your monitor in contrast and brightness to see all the different grey levels