Thursday, 6 February 2014

COMET - 17P Holmes

COMET - 17-P Holmes

Discovered: November 6, 1892
Epoch: October 27, 2007
Aphelion: 5.183610 AU
Perihelion: 2.053218 AU
Semi-major axis: 3.618414 AU
Eccentricity: 0.432564
Orbital period: 6.882994 a
Inclination: 19.1126°
Last perihelion: May 4, 2007
Next perihelion: March 22, 2014

Comet Holmes was a boring little object that sparked no particular interest until its visit in 2007 when it temporarily brightened by a factor of about half a million. It also became for a while the largest object in the solar system, and the 2007 event was the largest known outburst by a comet.

The comet had a similar outburst around the date of its discovery, when it brightened to mag 4 or 5 before fading into invisibility over a period of several weeks.

It is interesting to notice that the comet was "lost" for about half a century (between 1906 and 1964) before it was re-discovered by a lady working for the US Navy in Arizona.

Its nucleus was estimated at roughly 3.5 km and its coma expanded from little over 3 arcminutes to an impressive 13 arcminutes.

The images here show several comparisons between the apparent dimension of the comet, its evolution in time, and the Moon for reference.

Evolution of 17P-Holmes's apparent size as compared to Moon

Reports diverge as to the reason for the 2007 expansion. It is not the aim of this webpage to give in-depth astro-physical and chemistry explanations as to the phenomenon, but rather to show a few pictures of the event.
Magnitude 5 was recorded in February 2008, about the limit of what human eyes can see.

Comet 17P-Holmes (2007)

This is a bit of photoshop fun - hardly scientific but it does show the structure of the comet and interesting features in the coma.

Structure of 17P-Holmes: nucleus and coma

Holmes usually shined at an obscure mag 17 before brightening up to mag 2.8 in 40 hours or so (October 23 to 24), making it visible to the naked eye in Perseus: observers easily distinguished a fuzz in the sky even in heavily light-polluted skies.

Chance made it that the outburst coincided with opposition, making it even more spectacular. The position of the comet was such that observers on Earth were looking down its tail - its appearance was somewhat different of the "blob-and-tail" image one associates with comets. It was nicknamed the jellyfish comet because of the peculiar shape long exposures showed (NOT visible in my images here).

Overtime comparison with the Moon - the expansion was brutal and a delight for small instruments.

17P Holmes - Overtime comparison with the Moon 

The picture shows one of the first photographs I took of 17P Holmes, before the outburst reached its spectacular maximum, and gives its position relative to Perseus and Cassiopeia.

17P-Holmes before outburst maximum


And the blue one in negative - does show some structure.

17P-Holmes negative