The majority of objects in the deep sky database include the visual descriptions used by Johann Dreyer in his "New General Catalogue", published in 1888. These descriptions are remarkable for their information content, but can be somewhat daunting at first. For example, the Dreyer description of the globular cluster M3 in Canes Venatici is as follows:
GCL,eB,vL,vsmbM,*11This can be translated as "Globular cluster, extremely bright, very large, very suddenly much brighter towards the middle, composed of 11th magnitude stars" - a pretty good description in only 19 characters!
Similarly the galaxy NGC 2863 in Hydra is described as:
cF, S, E, bet 2 st 12, 16which means "considerably faint, small, elongated, between two stars of magnitude 12 and 16".
The description normally starts with a description of the object's brightness and size. Dreyer adopted the scale used for this from Sir John Herschel, and the order used may be confusing to modern observers; for example, is "considerably faint" brighter or fainter than merely "faint"? The other possible source of confusion is that 19th century astronomers often called a faint star "small" and a bright star "large", so one always has to be careful to judge whether a description such as "pretty small" refers to size or brightness!
The scale used is as follows:
Brightness Size eF Excessively faint eS Excessively small vF Very faint vS Very small F Faint S Small cF Considerably faint cS Considerably small pF Pretty faint pS Pretty small pB Pretty bright pL Pretty large cB Considerably bright cL Considerably large B Bright L Large vB Very bright vL Very large eB Extremely eL Excessively largeNext normally comes a description of object's general shape. This lies on a scale ranging from "round" to "extremely extended", as follows:
Code Shape R Round vlE Very little extended E Elliptic or oval cE Considerably extended pmE Pretty much extended mE Much extended vmE Very much extended eE Extremely extendedBy far the most cryptic part of the description, at first glance, is the group of letters giving what Sir John Herschel described as "the degree and rate of condensation". A simple example is "gbM", meaning "gradually brighter towards the middle". Looking, though, at NGC 4725, a galaxy in Coma Berenices, we find the dreadful looking "vsvmbMeBN"! Even this mouthful, though, is fairly easily translated as "very suddenly very much brighter in the middle, with an extremely bright nucleus".
When the descriptions give directions on the sky, the terms "preceding" and "following" are used for west and easy respectively. To see what is meant by this, picture the way an object drifts across the field of view of a telescope if the drive is switched off. Use of these terms is much more natural at the telescope eyepiece than the very confusing west and east, given the way that optical systems invert and/or reflect the field of view.
Quite often the notes speak of groups. The "1st of 4" is the first member of a group of four nebulae to drift across the field of view ie, the most western one, preceding all the others. All members of a group will have very nearly the same declination.
Ab..............about n..............north
alm.............almost neb............nebula
am..............among nf.............north following
app.............appended np.............north preceding
att.............attached nr.............near
b...............brighter N..............Nucleus, or to a
Nucleus
be..............between p..............pretty (before
F,B,L,S)
biN.............binuclear p..............preceding
bn..............brightest towards pg.............pretty gradually
the north side pm.............pretty much
bs..............brightest towards ps.............pretty suddenly
the south side P..............poor
bp..............brightest towards quad...........quadrilateral
the preceding side quar...........quartile
bf..............brightest towards r..............resolvable
the following side (mottled,not resolved)
B...............bright rr.............partially relolved,
c...............considerably some stars seen
ch..............chevelure rrr............well resolved, clearly
co..............coarse, coarsely consisting of stars
com.............cometic R..............round
cont............in contact RR.............exactly round
C...............compressed Ri.............rich
C.G.H...........Cape of Good Hope s..............suddenly
Cl..............cluster s..............south
d...............diameter sp.............south preceding
def.............defined sf.............south following
dif.............diffused sc.............scattered
diffic..........difficult st.............stars
dist............distance or sev............several
distant susp...........suspected
D...............double sh.............shaped
e...............extremely, stell..........stellar
excessively S..............small
ee..............most extremely sm.............smaller
er..............easily resolvable triN...........trinuclear
exc.............excentric trap...........trapezium
E...............extended v..............very
f...............following vv.............very, very
F...............faint var............variable
g...............gradually *..............a star: *10, a star of
gr..............group 10th magnitude
i...............irregular **.............double star
inv.............involved,involving ***............triple star
iF..............irregular figure !..............remarkable
l...............little,long !!.............very remarkable
L...............large !!!............a magnificent or
m...............much otherwise interesting
mm..............mixed magnitudes object
mn..............milky nebulosity st 9...........stars from the 9th
M...............middle, or in the magnitude downwards
middle st 9 13........stars from the 9th
to 13th magnitude
() items questioned by Dreyer enclosed in parentheses
" arc seconds (two "not-equals" in published catalog)
' arc minutes (one "not-equals" in published catalog)
See also NGC Abbreviations from the NGC/IC Project.