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THE ASTRONOMER Electronic Circular No 1058      1996 Mar 16 16.16UT
Ed:Guy M Hurst, 16,Westminster Close, Kempshott Rise,  Basingstoke,
Hants, RG22 4PP,England. Telephone/FAX(0256)471074 Int:+44256471074
INTERNET: GUY@TAHQ.DEMON.CO.UK             GMH at AST.STAR.RL.AC.UK
WORLD WIDE WEB                    http://www.demon.co.uk/astronomer
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COMET C/1996 B2 HYAKUTAKE
John Bortle, Stormville, USA e-mails (Mar 10):
"That C/1996 B2 will come to be remembered as the Great Comet of
1996 seems all but assured at this point. Its appearance at this
writing (Mar 7) is indeed that of a bright, intensely condensed
object which, at its present heliocentric distance, is the clear
signature of a truly major object on its way to perihelion. This
comet is certainly no Kohoutek or Austin and nothing of its
apparent calibre has approached so close to Earth in centuries. I
firmly believe that a really amazing, historic display is in the
offing.

An analysis of 22 selected magnitude determinations (from only the
very best observers), spanning the period February 1-March 7,
results in the photometric formula:
   m1 = 4.31 (+/-0.15 p.e.) + 5 log D + 11.78 (+/-0.68 p.e.) log r

>From this it seems safe to conclude that near perigee the comet
will attain a total magnitude of 0 to -1. Naked eye observers
should expect to see a parabolic coma at least 0.75-degrees in
diameter which will be intensely condensed and possess a striking,
almost stellar nucleus. Binoculars may well reveal long, multiple
rays in the plasma tail and telescopic observers should look for
distinct jet or fountaining structure projecting roughly sunward
from the nucleus.

Based on development up to the present, I would anticipate that
the plasma tail, although very faint, will become exceptionally
long for a few days either side of perigee. At that time the tail
could easily measure in the tens of degrees when observed from a
dark site. Because of our viewing angle, the plasma and dust
tails should be superimposed.

The circumstances governing the appearance and brightness of the
comet's dust tail are more complex. An interesting situation
occurs on March 28 UT, when the Earth will pass through the
orbital plane of C/1996 B2 (I make the nodal crossing to be
around 11 hours UT). This could result in an unusual event the
exact details of which are strongly dependent on the amount of
dust the comet has already laid down in its orbit. For a brief
interval when the Earth is near the comet's orbital plane, the
dust tail should become quite narrow and its apparent brightness
may be enhanced. A distinct, bright tail spine, possibly extending
well beyond the terminus of the normal dust tail, may briefly
become apparent. This would be because we will then be viewing
not only the dust tail proper but also any thin sheet of particles
already trailing the comet in its orbit.

As to the comet's behaviour during April, I do not think that with
its passage through perigee C/1996 B2's show is by any means over.
It seems likely that, following perigee, the comet will not drop
below +1 magnitude as it traverses the evening sky and a bright,
fairly well developed naked eye dust tail may be present during
the 2nd half of the month as the comet once again begins to gain
in brightness. Telescopic visibility during the daytime is a
distinct possibility very late in April and in early May, with
the comet perhaps becoming nearly as bright as did Comet West in
1976 (-3.0mg) as it rounds the Sun!"
Guy M Hurst