1. Introduction
FOR TWO DECADES,
starting in the late 1960's, the southern sky was patrolled by a dedicated South
African comet-hunter named Jack Bennett. He observed from his urban backyard
with a 5-inch low-power refractor. Not only did he discover two comets, he also
picked up a 9th magnitude supernova in NGC 5236 (M83), becoming the first person
ever to visually discover a supernova since the invention of the telescope.
Bennett was born on April 6th, 1914 and passed away on May
30th, 1990. A long-standing member of the Astronomical Society of Southern
Africa (ASSA), he was elected President in 1969. The Society awarded him the
prestigious Gill Medal for services to astronomy in 1970 and in 1986 he received
an Honorary Degree of Master of Science from the University of Witwatersrand. In
1989, at the recommendation of Rob McNaught of Siding Springs Observatory, the
asteroid VD 4093 was named after him.
Bennett was a skilled observer and in the spirit of Charles
Messier drew up two lists of southern objects that appeared comet-like in his
telescope. His first list (Bennett, 1969) was published four months before he
discovered his first comet. The supplementary list (Bennett, 1974) was followed
three months later by his second discovery.
In his 1969 Presidential Address to the ASSA Bennett said: "As
an aid to the recognition of comet-like objects in the Southern sky, and to help
observers to eliminate them in comet searches, I have over the past five years
compiled a list of 130 such objects visible south of the celestial equator.
Nearly a hundred of these have been encountered under varying conditions in
comet sweeps using a 5-inch short-focus refractor with a magnification of 21
diameters. The rest have been added, and duly observed with the same telescope,
after consulting various sources, notably E. J. Hartung's first-rate book
'Astronomical Objects for Southern Telescopes' which includes details of the
appearance in telescopes of various apertures of all but 16 of the 130 objects."
Bennett's 1974 article "Some objects of interest in the
southern sky" introduced 22 new comet-like objects "which had been
observed (many of them repeatedly) in comet sweeps" since his first list
was published.
These two lists have been combined to form the Bennett
Catalogue (Table 1). Bennett's list reads like the "Who's Who of the
Deepsky". Among the 152 objects are the Tarantula, Omega Centauri, 47
Tucanae, Sombrero and the Silver Coin. Twenty-six of Messier's objects are
listed. Bennett noted that including such bright objects may be unnecessary, but
added: "it is surprising how easily even these can be mistaken for comets
when seen at low altitudes and poor conditions."
Almost half the objects in Bennett's list are globular
clusters, which makes sense since these bear a striking resemblance to comets.
The constellation richest in Bennett objects is Sagittarius, followed by
Ophiuchus. Bennett wrote that "the constellations Scorpio, Ophiuchus and
Sagittarius . . contain a bewildering variety of comet-like objects. These are
mostly globular clusters and all except the largest defy attempts to distinguish
them from tailless comets. This relatively small area of sky contains about a
third of all the comet-like objects visible with small telescopes south of the
equator."
Dorado also contains many Bennett's - five galaxies and six
clusters and nebulae. The latter lie within the Large Magellanic Cloud which,
according to Bennett, "should normally be avoided like the plague by anyone
looking for comets. There are, however, a few objects on the outskirts of the
Clouds which are regularly encountered in comet sweeps, and these have been
included in the list, if only as a warning to the observer of the perils that
lie ahead of him!" |