Comet Holmes
17P/Holmes is a periodic comet of the Jupiter family. The orbit of the comet passes between Mars and Jupiter with an orbital period of about seven years.
Discovery history
On November 6, 1892 British amateur astronomer Edwin Holmes discovered in the vicinity of the Andromeda nebula shortly before midnight a comet, but its exact position he was able to determine, due to the dense cloud cover after midnight - this circumstance means that sometimes November 7 is specified as a detection timing.
The comet was visible during the entire month of November with the naked eye. In mid-January 1893 comet was only an object about 10 size class before its brightness again reached the area of 8th mag. Since the comet the sun never comes closer than the planet Mars, the discovery is due to an outburst.
1899 and 1906 came 17P/Holmes back in the sun next part of its orbit, taking each remained an extremely light faint object. After 1906 he was no longer found and was long considered lost. In 1963, Brian Marsden was due to new track calculations to the conclusion that the orbit of the comet must have changed. With the new path data 17P was then rediscovered in 1964 and has since been regularly observed.
Outburst in 2007
On 4 May 2007 17P again reached the point nearest the Sun its path. Since its brightness had dropped to below 16 mag. In the early morning of October 24, 2007 announced an observer on Tenerife that the comet was much brighter than expected. Shortly thereafter, Bob King estimated the brightness of Minnesota from 7.1 mag. A few hours later, the same observers already see him as an object 4 size class with the naked eye. Once again 6 hours later was reported by Japanese and Italian observers with a brightness of 2.8 like; on the night of 24 to 25 October 2007, reported from North America 2.6 mag. 17P has increased its brightness within a very short time to the 500,000 -fold. Since the outbreak of the diameter of the coma increases by 97,000 km / day, ie the radius changes by 0.56 km / s (7 November 2007). On November 9, 17P was the largest object in the solar system before the sun.
The cause of this outbreak may be a collision with a larger boulders breaking up the surface or even the breakup of the comet. As a result, large quantities of dust are released. As it turns out in spectroscopic analysis, the sunlight is reflected in this material. However, a specific trigger which has released the dust is not known.
17P/Holmes was early November 2007 1.60 AE (242 Mio.km ) away from the earth and to find in the constellation Perseus. With the naked eye it was realized a slightly yellowish " Nebula ". The telescope was in the center rather whitish, greenish outside coma with an apparent diameter of about 40 arcmin visible ( true diameter of more than 2 million km). In the course of 17P has developed a recognizable already with strong binoculars tail; this appeared at that time very short, as it points away almost exactly from the earth. Holmes ' brightness was on 5 November 2007 unchanged at about 2.5 like with very slight downward trend. On 20 November 2007 he had already reduced its brightness to 3.1 mag.
Also in February 2008, the comet was still observable. The brightness was, however, dropped to magnitude 5.0.