Millennium Comet
Washington University
Gary W. Kronk
1995 Aug. 3
C/1995 O1 (Hale-Bopp)
(Orbit on IAUC 6198)
- Green issued IAUC 6191 on July 26, which gave the first orbit computation (listed as
highly uncertain). Based on 57 positions obtained on July 24-26, it indicated the comet would pass
perihelion in early 1997!
- Brian Marsden (Central Bureau for Astronomical Telegrams) issued IAUC 6194 on August 1.
It gave a parabolic orbit based on 208 positions obtained during the period of July 24 to August 1. This
new orbit, which is still considered "somewhat uncertain", had a perihelion date of April 1, 1997, and a
perihelion distance of 0.9 AU.
- McNaught's prediscovery image was announced on IAUC 6198 and enabled Marsden to
compute a very precise orbit. This new orbit indicated the general correctness of the orbit on IAUC 6194,
except that the comet is moving in a long-period ellipse. It currently has an orbital period of about 4000
years, but the original orbit may have had a period of about 3200 years. Marsden comments that comet
Hale-Bopp "is not on its first pass from the Oort Cloud."
- Marsden wrote on IAUC 6202, "Taking the situation at face value, one can note that comet
C/1995 O1 is in many respects similar to the great comet C/1811 F1 (early absolute brightness,
perihelion distance, orbital inclination, 3000-year revolution period, placement beyond the sun at
perihelion) and may perform as spectacularly."
