Comet Hale-Bopp was discovered on July 23, 1995 by Alan Hale and Thomas Bopp at a distance from the sun of about 7 AU with an apparent magnitude of 10.5, which is extremely bright for a comet at such a distance. This corresponds to a diameter of more than thousand kilometres should we see the bare nucleus, which is not the case since an extended coma has been detected, and is clearly visible in the above image. The actual size of the nucleus is difficult to determine because it is hidden within the coma. Another explanation for the unusual brightness might be that the comet experienced an outburst which increased its brightness by several magnitudes. Observations during the coming months will show whether the comet is fading or not.
Extensive astrometric observations in the days after the discovery (more than 200 in 3 days) and a prediscovery identification by Rob McNaught on a UK-Schmidt plate taken in April 1993 allowed a rapid orbit determination.
C/1995 O1 has an orbital period of about 2500 years, an inclination of nearly 90 deg, and a perihelion distance of 0.9 AU (MPC 25513). According to Brian G. Marsden (Minor Planet Center), this comet resembles in many respects the great comet of 1811, and it might perform as spectacularily.
Ephemeris calculations, based on the current orbital parameters and the assumption that the comet's brightness is not biased by an outburst, predict an outstanding appearance in April 1997. The comet should be visible for observers in the northern hemisphere in the evening sky shortly after sunset, reaching a brightness of -1.7 mag (IAUC 6202).
Comet 1995 O1 Hale-Bopp - observed on April 4, 1997 by Tarmo Oja at the Kvistaberg observatory, Sweden. 100/135/300 cm Schmidt telescope with 4.5 min exposure time, on 4415 baked film.
Comet 1995 O1 Hale-Bopp - observed on August 31, 1995 by Mats Dahlgren (Uppsala Astronomical Observatory) and Felix Lahulla (Observatorio Astronomico Nacional, Madrid) using the 90cm Dutch telescope at ESO (La Silla, Chile). See also the ESO Press Photo 26/95, 5 September 1995.
Comet 1995 O1 Hale-Bopp - observed by Anders Erikson (DLR, Institute of Planetary Exploration, Berlin) using the 60cm Bochum telescope at ESO (La Silla, Chile) and the DLR CCD camera system with a 1024x1024 Tektronics chip.
The comet is clearly visible to the naked eye!
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