It has been reported that periodic comet Holmes 17P brightened over one million-fold over the course of a single day by the end of October, with backyard astronomers all over the world observing the new star in the Perseus constellation on October 24, 2007. Erupting from a very dim magnitude 17 to about magnitude 2.5, its star like nucleus instantly expanded into a round little disk, visible to binoculars and telescopes as nothing every seen before.
Yet in the middle of October, it had been simply a nonentity in between the orbits of Jupiter and Mars. Up until recently, no one know exactly what caused such an event, but scientists lately have been able to train the Hubble Wide Field Planetary Camera 2 on Comet Holmes in an attempt to shed light on what was actually happening with it.
The very first time the Hubble telescope actually looked at Comet Holmes was back in 1999, a time when the comet's nucleus of the comet was too small to measure it directly. At that time, astronomers had the ability to infer the nucleus' diameter. This was done by measuring it through its brightness, which was approximately 3.4 kilometers, which according to the November 18, 2007, Nobel Intent article, is about the distance between the Arc de Triomphe and the Louvre glass pyramid in its courtyard.
Recent imagery sent out by the Hubble show three spurs of dust, along with a dust outburst west of the nucleus. But what they do not show is the clear reason for its tremendous brightening. Another comet, Schwassmann-Wachmann 3 (SW3), at another time was observed by the Hubble as it ejected a number of mini-comets after a similar brightening. The images from the ground of Holmes seem to possibly suggest that a large piece has broken off-resulting in some of the excess brightness, with it disintegrating into dust. But the images from space refuse to allow the Hubble to spy any of these broken-off pieces, due to its large distance from the planet Earth (1.6 AU). Yet none of this has been proved as confirmation other than in theory alone.
In November of 1892, the Holmes comet was seen also as a major eruption similar to that of today, with English amateur, Edwin Holmes, the first individual to see it. It reached a 4th and 5th magnitude only to fade in the following weeks with a second eruption occurred 2.5 months after this. Holmes was a regular observer of the M31 galaxy, referred to as the Andromeda, and saw a comet with a coma about five arc minutes across, with an unparalleled bright nucleus.