Messier Catalog Column Descriptions
Heading Description   Heading Description
M Messier Catalog Number   RA Right Ascension (J2000) in Hours and Minutes
NGC New General Catalog Number   Dec Declination (J2000) in Degrees and Minutes
Type Celestial Object Classification (see table below)   Con IAU Constellation Abbreviation
Mag Apparent Visual Magnitude   Viewing
Best Season for Viewing Messier Object
Size Angular Size in Arc-Minutes   Common
Informal or Colloquial Name of Messier Object
Distance Distance from Solar System in Light Years      
  Messier Catalog Category Descriptions
Type Description   Type Description
OC Open Cluster   SP Spiral Galaxy
GC Globular Cluster   BA Barred Galaxy
PL Planetary Nebula   LN Lenticular Galaxy
DI Diffuse Nebula   EL Elliptical Galaxy
AS Asterism   IR Irregular Galaxy
DS Double Star   SN Supernova Remnant
MW Milky Way Patch