Author: 丛雨

The Messier Catalogue

  Of all deep-sky catalogues, the Messier Catalogue is probably the best known. Compiled under the direction of French astronomer Charles Messier, it contains 110 deep-sky objects: 12 nebulae (M1, the Crab Nebula, is the only supernova remnant in the catalogue), 57 star clusters (28 globular and 29 open clusters), 40 galaxies, and one double star, M40, included by mistake. Many objects familiar to amateur astronomers are Messier objects, including the Andromeda Galaxy (M31), the Orion Nebula (M42), and the Pleiades (M45). Messier was in fact an enthusiastic comet hunter. During his searches, he encountered objects that looked like comets but were not, prompting him to compile the catalogue first published in 1771. His original list contained only 45 objects. By 1781, observations made by Messier and Pierre Méchain had expanded it to 103, and later astronomers completed the catalogue. Messier worked in France and naturally could not observe targets across the entire sky, so all Messier objects lie north of roughly −36° declination. The list is especially well suited to observers in the Northern Hemisphere. Around late March each year, many astronomy enthusiasts choose a clear, moonless night for a “Messier marathon,” attempting to find every object in a single night with a telescope.

Messier objects

The Caldwell Catalogue ©

  The Caldwell Catalogue is less famous than the Messier list. It contains 109 comparatively bright deep-sky objects in both the northern and southern skies that do not appear in the Messier Catalogue. These comprise 25 nebulae—including two supernova remnants, one dark nebula, and 13 planetary nebulae—43 star clusters, 35 galaxies, and six objects combining a cluster and a nebula. The catalogue was compiled in 1995 by British amateur astronomer and science writer Sir Patrick Caldwell-Moore. Better-known entries include the Double Cluster in Perseus (C14) and the Hyades in Taurus (C41), as well as southern objects less familiar to many northern observers, such as the Carina Nebula (C92) and the globular cluster 47 Tucanae (C106). Because the Caldwell Catalogue was designed to complement Messier’s, no object in it carries an M number, and vice versa. It includes many objects in the southern sky whose full appearance can be difficult for observers in the Northern Hemisphere to explore.

Caldwell objects

New General Catalogue of Nebulae and Clusters of Stars (NGC)

  Apart from Messier numbers, NGC designations are probably the deep-sky identifiers encountered most often. This famous catalogue contains 7,840 nebulae, star clusters, and galaxies. Nearly every familiar deep-sky object has an NGC number: the Andromeda Galaxy, for example, is both M31 and NGC 224. The earliest NGC data came from observations made at Dunsink Observatory by William and John Herschel and other members of Britain’s Royal Astronomical Society. John Dreyer first organized and compiled the material in 1880. The initial NGC data contained some errors and has since undergone repeated checking and correction, including the publication of the Revised New General Catalogue (RNGC).

Index Catalogue of Nebulae and Clusters of Stars (IC)

  Usually called the Index Catalogue, the IC extends and supplements the NGC with another 5,386 objects. It consists of IC I and IC II, completed by Dreyer in 1895 and 1905 respectively. The Horsehead Nebula in Orion (IC 434) is one familiar IC object. Likewise, no object has both an NGC and an IC designation.

  The following list briefly introduces several other catalogues of galaxies, nebulae, and star clusters, without going into detail.

  • Uppsala General Catalogue (UGC): 12,921 galaxies, almost all in the northern sky
  • Catalogue of Galaxies and Clusters of Galaxies (CGCG)
  • Morphological Catalogue of Galaxies (MCG)
  • Principal Galaxies Catalogue (PGC): includes both the Large and Small Magellanic Clouds
  • Atlas of Peculiar Galaxies (Arp): 338 morphologically unusual galaxies, including galaxies undergoing collisions and mergers
  • Sharpless catalogue of bright nebulae (Sh2): 313 emission nebulae
  • RCW Catalogue: 180 emission nebulae, mainly in the southern sky
  • Gum Catalogue: 85 emission nebulae, mainly in the southern sky
  • Lynds’ Catalogue of Bright Nebulae (LBN) and Lynds’ Catalogue of Dark Nebulae (LDN)
  • van den Bergh Catalogue of Reflection Nebulae (vdB): 158 reflection nebulae
  • Barnard Catalogue of Dark Markings in the Sky (B): 350 dark nebulae
  • Melotte Catalogue of Star Clusters (Mel): 245 star clusters