This pages contain the results of visual and CCD observations of comet
Hyakutake, obtained at the Crni Vrh Observatory as well as observations
from M. V. Zanotta (Milano) and some other Italian groups.
Except otherwise noted, observations are by H. Mikuz, Crni Vrh Observatory, Slovenia
KEY TO ABBREVIATIONS
Comet Hyakutake (C/1996 B2) Photometry obtained with 20-cm, f/2 B-S camera, V filter and ST-6 CCD.
1996 Feb. 18.15UT: V=7.8, Elliptical coma ~14'x16' DC=7. Delicate tail ~0.3o in ~PA 280o. 1996 Feb. 27.15UT: V=6.7, Elliptical coma ~20'x25' DC=7. Faint, diffuse tail ~1o in PA ~290o. Further 3-min R image shows similar ~1o fan-like tail in PA ~270-290o. 1996 Mar. 1.16UT: V=6.3, Elliptical coma ~24'x28' DC=7. Comet has ~0.7o diffuse tail in PA ~285o. 1996 Mar. 3.17UT: V=5.9, Elliptical coma ~24'x28' DC=7. 1996 Mar. 6.16UT: V=5.6, CDia=~20' DC=7. Moonlight.Naked-eye m1 estimates
1996 Mar. 21.10UT: m1=1.5, CDia=~60' DC=7. Tail ~20 deg long in PA ~260o Star-like c. cond. clearly visible with naked eye. Very good conditions! 1996 Mar. 27.10UT: m1=0.4, CDia=~60' DC=7. Straight tail extending for ~45deg, until Beta CVn. Limiting mag. 6.5. Comet and stars defocussed with spectacles. In 15x80B the coma appears of distinct greenish color with star-like nuclear condensation. With the same instrument, straight narrow jet ~3deg long was visible, spanning from the comet c. cond. in PA ~145deg. 1996 Apr. 05.80UT: m1=2.9. Tail about 6 deg. Naked eye estimate, using the convex lens (comet appears as a stellar source) 1996 Apr. 5.80UT: m1=2.9, CDia=~15' DC=7. Straight tail ~10deg in PA 45deg. (7x50B) 1996 Apr. 6.82UT: m1=3.1, CDia=~12' DC=7-8. Tail ~11deg in PA 44 deg. (7x50B)Photometry obtained with 2.8/35mm lens, V filter and ST-6 CCD.
1996 Apr. 7.82UT: V=2.8, CDia=~20' DC=8-9. Tail length at least 14 deg (frame edge). 1996 Apr. 9.82UT: V=2.8, CDia=~20' DC=8-9. Mosaic frames were taken around Apr. 9.82UT in order to determine the full length of comet tail. It may be traced up to 22o from the comet nucleus. Straight, narrow tail of rather uniform surface brightness is present from the nucleus distance ~10o to 22o. Take a look at Hyakutake images page. 1996 Apr. 15.81UT: V=1.9, CDia=~10' DC=8-9. Tail ~15deg in PA 40 deg. 1996 Apr. 17.80UT: V=2.4, CDia=~10' DC=8-9. Tail at least 15deg in PA 37 deg. 1996 Apr. 18.82UT: V=2.6, CDia=~ 8' DC=8-9. Tail at least 15 deg. 1996 Apr. 19.81UT: V=2.8, CDia=~ 8' DC=8-9. Tail at least 15 deg. 1996 Apr. 20.81UT: V=2.7, CDia=~ 8' DC=8-9. Tail at least 15 deg. 1996 Apr. 21.81UT: V=2.7, CDia=~ 6' DC=8-9. Tail at least 15 deg.Visual m1, coma-diameter and tail-length estimates by Mauro Vittorio Zanotta (Italy)
Unless otherwise stated, these are naked-eye estimates.
1996 Mar. 23.02UT, 1.0, 1.7 deg, 20 deg Breuil-Cervinia, Italian Alps (2100m) 24.06, 0.8, 1.9 deg, 30 deg 25.00, 0.5, 2.0 deg, 40 deg 28.13, 1.1, 65' 60 deg (Monte Generoso) 29.14, 1.3, 55' 45 deg 30.14, 1.5, 45' 35 deg 31.14, 1.6, 40' 30 deg Apr. 6.82, 2.2, - 9 deg 7.82, 2.2, - 9 deg 9.82, 2.2, - 15 deg (San Marco Pass) 12.82, 2.2, - (Monte Generoso) 13.82, 2.2, - 14.82, 2.1, - 18 deg 15.82, 1.8, - ( Milano) M. Zanotta writes: "In 25x150 binoculars, amazing colors were visible inside the coma. The brighter parabolic envelope was yellow/green, the outer diffuse halo fluorescent blue and the tail was of white color". Apr. 16.82, 1.8, - 18 deg/gas 12deg/dust (San Marco Pass) In 25x150B easy streamers and dark lines in the gas tail. Apr. 18.82, 1.7, - 10 deg (Mount Mottarone) 19.82, 1.7, - 10 deg (San Marco Pass) 19.82, - - 22 deg tail in PA 41 deg (7x42B) 20.82, 1.9, - (Milano, 7x42 binoculars). 21.82, 1.9, - (Milano, 7x42 binoculars). 24.81, 1.8, - (Milano, 7x42 binoculars).Wide-field CCD observations with narrow-band filters
1996 Mar. 3.18UT: 10-min wide-field CCD exposure, taken with the Zeiss 2.8/180mm lens and narrow-band H2O+ filter centered at 620nm (FWHM=10nm) shows ~3o delicate ion tail in PA ~293o. 1996 Mar. 10.958UT: Two co-added wide-field CCD exposures of 12 min total duration, taken with the Zeiss 2.8/180mm lens and narrow-band H2O+ filter at 620nm (FWHM=10nm), shows at least ~4deg ion tail in PA ~285o. There is conspicious disconnection in tail, between the nucleus distance 1.0-1.4deg. 1996 Mar. 20-21: Series of wide-field images were taken at the Crni Vrh Observatory in very good conditions with the 180mm and 65mm lenses, CCD and narrow-band filters. The mosaic image, taken on 1996 Mar. 20.94UT with the H2O+ filter, centered at 620nm (FWHM=10nm) shows numerous streamers in the sector PA 245-275o, some of them extending up to ~7o from the nuclear region. Also there is conspicious disconnection in ion tail at nucleus distance 137'. Further mosaic frames taken around 1996 Mar. 21.09UT display at least ~20o complex ion tail structure with kinks, clouds and knots of material along the main tail stream in PA 260o. There is a bifurcation at nucleus distance ~7o. Additional imaging with the same lenses and red continuum filter, centered at 647nm (FWHM=10nm) shows ~7o broad, diffuse and slightly curved dust tail in PA ~250o. 1996 Apr. 6: Series of narrow-band CCD images were taken at the Crni Vrh Observatory in very good atmospheric conditions. The 90mm f.l. frames, obtained in the light of singly-ionized water ions shows numerous streamers, extending up to ~5deg from the nuclear region. Mosaic images revealed several knots of material along the main tail stream. The ion tail total length on 65mm f.l. images, is about 15 degrees. A remarkable kink is present at nucleus distance 6.0deg. At this point, the tail PA is turning from 44deg to 50deg. Additional monitoring with red continuum filter display ~8 deg broad dust tail.
Reports from the Italian and Slovene observers for the Mar. 23-25 nights
Antonio Milani writes: I observed from a dark site at Mt.
Grappa (1650 m), Italy on Mar. 24-25. Clouds ended around 1400-1500 m and
the top of the mountain was clear. The cloud layer covered nearly all the
light from the nearby plane, allowing to have a very dark sky. I estimated
m1= +0.2, coma diameter nearly 2 deg. With a strong condensation the tail
was easy to see for 40 deg but with averted vision it was detectable at
least for 50 deg. A wide angle photograph by Eraldo Guidolin shows at least
a 60 deg. tail. The tail had a very smooth wavy "S" shape and
showed a noticeable evolution during the night.