Comet 17P/Holmes was discovered by E. Holmes of London, England. Holmes regularly observed the Andromeda galaxy or the M31. On November 6, 1892 evening, after making some observations on Jupiter in a sky that was not very conducive to sky watching, Holmes directed his 32-cm reflector telescope to a group of faint companions of Mu Andromeda and the nearby M31 galaxy as for one last look at the sky.
What he thought to be the M31 turned out to be something different. It was a comet, to be later named comet 17P/Holmes, with a coma of about 5 arc minutes. An arc minute is the unit used to measure the diameter of the coma and length of the tail of comets and other objects in the sky. Jupiter at its brightest measures 0.8 arc minutes.
Holmes made another observation on the next day and marked its position and immediately informed E.W. Maunder of the Royal Observatory at Greenwich, England, W.H. Maw in England and Kidd in Bramley, England. Kidd was a bit sceptic in the beginning. But he observed it along with Bartlett with naked eye and there were also independent sightings by T.D. Anderson of Edinburgh, Scotland and J.E. Davidson in Mackay, Queensland, Australia. Thus, the existence of comet 17P/Holmes was known by the world.
The first orbit of the comet 17P/Holmes was calculated by H.C.F. Kreutz. Another set of findings about the comets orbit was calculated by E. Weiss and A. Berberich. Though these orbits did not match the calculation of Kreutz, they seemed to fit the comet perfectly. Kreutz himself found conflicting results on later observations. The peculiarity was observed by many astronomers who came to the conclusion that it might be the lost comet 3D/Biela. Later observations were finally able to establish the perihelion date as June 13 and the period to be 6.9 years.
Though comet 17P/Holmes was observed past its perihelion date, its visibility was assigned to the outbursts recorded in November and then in January next year. The comets return was predicted by E. Kohlschutter and H.J. Zwiers. The comet was again sighted by C.D. Perrine of Lick Observatory of California in 1899 with only a minor correction to Zwiers prediction.
After many observations in the later return of the comet 17P/Holmes, its final perihelion distance was increased from 2.121 AU to 2.347 AU and the orbital period was corrected to 7.35years from 6.86 years. The calculations were made by B.G. Madisen using a high-speed computer in 1975.
The appearance of comet 17P/Holmes in 2007 was marked by a sudden outburst. On its first appearance in July it was of magnitude 14.5. But within few hours of October 24and 25 it grew from magnitude 7.1 to 2.6 naked-eye magnitude. Through the whole of remaining October many observers of the comet reported that it has been holding the latest magnitude of 2.6 to 2.8.
Cometography
