It's funny you should ask that. When McNaught was doing its thing, I put
together a ranked list of the 'Great Comets' of the previous two centuries
(later extended back to AD 1550) by adding together numeric scores for various
cometary attributes. The numbers were entirely arbitrary, and if I were to redo
the list I would certainly change the scores I awarded certain attributes (the
system tends to under-rate the bright sungrazers), but it does yield a
relatively impartial list of Great Comets.

Here is the methodology and ranked list of Great Comets I made at the time, with
Lovejoy added with the numbers it had earned as of yesterday (it is likely to
increase a few more points before it is done):

Here is a list I made for my own amusement some time ago, of the greatest
naked-eye comets of the last two centuries, visible to observers in the northern
temperate regions. I used a points system as follows:

MAGNITUDE: 10 points for every degree of magnitude brighter than +3 (dark-sky;
daytime magnitude gets counted separately)

TAIL: 1 point for every two degrees of length of naked-eye visible tail in dark
sky

DURATION VISIBLE: 1 point for every month naked-eye visible in dark sky

BONUS POINTS:
2 visible tails (dust tail and ion tail) = 10 points
5 visible "tails" (West 1976) = 20 points
15 degree long "anti-tail" (Arend-Roland 1957) = 10 points
curved tail (Donati 1858) = 5 points
'bright' tail (Daylight 1910) = 10 points
'brilliant' tail (Ikeya-Seki 1965, Great September 1882) = 20 points
circumpolar all night (Hyakutake 1996, Tebbutt 1861) = 10 points
Mag. -3 in daylight (West 1976) or Mag. -5 in daylight (Daylight 1910) = 10
points
Mag. -8 in daylight (Great March 1843) = 15 points
Mag. -15 in daylight (Ikeya-Seki 1965) or Mag. -17 in daylight (Great September
1882) = 30 points

123 pts 1861 Tebbutt
105 pts 2007 McNaught
101 pts 1882 Great September Comet
95 pts 1910 P/Halley
90 pts 1976 West
78 pts 1996 Hyakutake
73 pts 1997 Hale-Bopp
68 pts 1858 Donati
64 pts 1965 Ikeya-Seki
61 pts 1970 Bennett
57 pts 1957 Arend-Roland
54 pts 1910 Daylight Comet
52 pts 1811 Great Comet
52 pts 2011 Lovejoy
51 pts 1927 Skjellerup-Maristany
50 pts 1843 Great March Comet
46 pts 1874 Coggia
42 pts 1881 Great Comet
37 pts 1807 Great Comet
37 pts 1853 Klinkerfues
35 pts 1835 P/Halley
35 pts 1957 Mrkos
31 pts 1860 Great Comet
29 pts 1911 Beljawsky
28 pts 1911 Brooks
25 pts 1819 Tralles
24 pts 1854 Great Comet

Here is the same list in reverse chronological order:

52 pts 2011 Lovejoy
105 pts 2007 McNaught
73 pts 1997 Hale-Bopp
78 pts 1996 Hyakutake
90 pts 1976 West
61 pts 1970 Bennett
64 pts 1965 Ikeya-Seki
57 pts 1957 Arend-Roland
35 pts 1957 Mrkos
51 pts 1927 Skjellerup-Maristany
29 pts 1911 Beljawsky
28 pts 1911 Brooks
95 pts 1910 P/Halley
54 pts 1910 Daylight Comet
101 pts 1882 Great September Comet
42 pts 1881 Great Comet
46 pts 1874 Coggia
123 pts 1861 Tebbutt
31 pts 1860 Great Comet
68 pts 1858 Donati
24 pts 1854 Great Comet
37 pts 1853 Klinkerfues
50 pts 1843 Great March Comet
35 pts 1835 P/Halley
25 pts 1819 Tralles
52 pts 1811 Great Comet
37 pts 1807 Great Comet

Here is a (partial) list of the most notable Great Comets from the 250 years
prior to this list. Details are much sketchier, of course, and for the first
portion of this time period we have few or no records from the southern
hemisphere, so I expect that the list is incomplete, but the five comets listed
are surely among the top Great Comets of that time period. These numbers are a
minimum, I do not know if their ion tails were visible -- if so, that's another
10 points.

1577 (Brahe) : 80 degree tail; magnitude -3 in dark sky; reached magnitude -8 in
daylight; visible for 3 months; 'brilliant' tail = 138 points

1618 : 104 degree tail; magnitude -0.5; visible for 2 months = 89 points

1680 (Kirch) : 90 degree tail; magnitude 1.5 under dark sky; sungrazer (but not
a member of the Kreutz family) visible in daytime (no magnitude estimate -- I am
assuming -3); noted for bright tail; visible for 3 months = 83 points

1744 (Klinkenberg) : 90 degree tail; magnitude -3 under dark-sky(ish)
conditions; magnitude -7 daylight comet; 6 "tails" visible; visible for 4 months
= 144 points or more

1769 (Messier) : 97 degree tail; magnitude 0 under dark-sky conditions;
magnitude -6 daylight comet; visible for 3 months = 91 points (possibly more,
depending on the brightness of the tail)

Bill

Edit -- The number of Really Great Comets (80 or more points) in the nineteenth
and twentieth centuries is four, giving an average recurrence interval of 50
years, so in 250 years you would expect about 5 comets, if that rate is typical.
So there may be another Really Great Comet in the years from 1550 to 1800, most
likely from the first half of this time span and only visible in the southern
hemisphere, and hence unrecorded -- or there may not.

The top ten recorded comets of the past 450 years:

144 pts 1744 Klinkenberg
138 pts 1577 Brahe
123 pts 1861 Tebbutt
105 pts 2007 McNaught
101 pts 1882 Great September Comet
95 pts 1910 P/Halley
91 pts 1769 Messier
90 pts 1976 West
89 pts 1618 Great Comet
83 pts 1680 Kirch

And in reverse chronological order:

96 pts 2007 McNaught
90 pts 1976 West
95 pts 1910 P/Halley
101 pts 1882 Great September Comet
123 pts 1861 Tebbutt
91 pts 1769 Messier
144 pts 1744 Klinkenberg
83 pts 1680 Kirch
89 pts 1618 Great Comet
138 pts 1577 Brahe

--- In comets-ml@yahoogroups.com, dfischer@... wrote:

> E.g. as a Lovejoy-deprived Northerner I would really like to know how this one
'compares' to Hale-Bopp at its best. Or how McNaught compared to the Greatest
Comets in recorded history. The question is thus: Can one compress the overall
sight of a comet, coma AND tail, into just one somewhat reliable and
reproducible number?

Dan