17P/Holmes

October 24th 2007	:	A most amazing eruption occurred on comet 17P/Holmes. Normally at magnitude 17 the comet brightened to magnitude 3 in just a few hours and is easily visible to the naked eye. During this outburst the comet is near to its opposition with respect to Earth (see below simulation). This means that, since comet tails point away from the Sun, we are looking nearly straight down along its tail making it appear as a bright sphere in telescopes.

Path of comet 17P/Holmes

October 28th 2007	:	The comet looks like a bright, yellow star, and only magnification reveals a fuzzy coma around the dusty core. The comet reached magnitude 2,3 and its coma had grown to 5 arc minutes, at a distance of appr. 1,63 AU this means a coma diameter of about 0,34 million km.

October 30st 2007	:	The comet looks like a magn. 2,3 "fuzzy" star next to Alpha and Delta Persei while its coma is approaching 8 arc minutes, at a distance of appr. 1,63 AU this means a coma diameter of about 0,54 million km.

Overexposed nucleus and coma with green gaseous outer coma

The nucleus and tail of 17P/Holmes (mouse over for description)

November 11th 2007	:	After two weeks of clouds and rain finally a clear sky. Comet 17P/Holmes coma grew to stunning 24 arc minutes decreasing its surface brightness in spite of its constant magnitude (2,8). At a momentary distance of 1,62 AU to Earth this means a comet diameter of about 1,64 million km. The change rate can then be estimated at about 95.000km (~1,36 arc minutes) per day or a stunning dust ejection velocity of about 2000km/hr (~550m/s).

17P/Holmes and its 24' coma

November 12th 2007	:	Comet 17P/Holmes coma grew further to 25 arc minutes further decreasing its surface brightness in spite of its constant magnitude of 2,8. At a momentary distance of 1,62 AU to Earth this means a comet diameter of about 1,72 million km.

17P/Holmes and its rapidly growing coma

During the time between the images made on 11-11-2007 and 12-11-2007, in total 23 hours, the comet moved 11.4 arc minutes which means, at a distance of 1,623 AU, that the orbital velocity was approximately 35000km/hr (see below).

The movement of 17P/Holmes in the last 23 hours

November 15th 2007	:	Again a very cloudy night with some clear gaps arround midnight. These gaps where just long enough to image Comet 17P/Holmes again. The coma is still growing and is now 29 arc minutes further decreasing its surface brightness in spite of its slowly decreasing magnitude of 3,0. At a momentary distance of 1,63 AU to Earth this means a comet diameter of about 1,93 million km. The comet is now rappidly approaching the bright star Mirfak (alpha Persei). On November 19th Mirfak appears to be swallowed by the coma of the comet.

17P/Holmes approaching bright star Mirfak (alpha Persei)

November 17th 2007	:	Because the coma of comet 17P/Holmes remains growing, decreasing its surface brightness furthermore, she is hardly visible with the unaid eyes now from my light polluted urban area. The coma diameter is now 32 arc minutes, approximately the same angular diameter as full moon, or 2,12 million km which makes it by far the biggest object in our solar system.

17P/Holmes close to Mirfak (alpha Persei)

November 21th 2007	:	Because of covered skies I missed the "swallowing" of Mirfak by comet Holmes. The coma diameter measures now 38 arc minutes (2,6 million kilometer) decreasing its surface brightness furthermore. The comet was even not visible in my 7x50 viewfinder because of the 88% moon and high humidity.

17P/Holmes close to Mirfak (alpha Persei)

The angular diameter of the dust coma is changing extremely linear in time with an average change rate of about 1,30 arc minutes per day. The measured angular diameters from above images are plotted in below graph and connected by a trendline (see below).

The magnitude of comet 17P/Holmes was quite stable just after the outburst but started to decrease slowly since the first week of November. The surface brightness is decreasing due to the rapidly growing appearend diameter (see below graph).