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C/2004 K3 (LINEAR)

S indicates direction of Sun.

2004 May 31
00:08-00:20 & 01:40-01:53 UT
Mag +18.8, 42 x 22 second exposures (total exposure 15m 24s)
Motion 8.6"/min in p.a. 342
2004 June 07 00:18-00:45 UT
Mag +18.5, 45 x 22 second exposures (total exposure 16m 30s)
Motion 7.7"/min in p.a. 327
2004 June 08 00:12-00:42 UT
Mag +18.5, 45 x 24 second exposures (total exposure 18m 00s)
Motion 7.4"/min in p.a. 322
2004 June 27 22:48-23:09 UT
Mag +18.4, 28 x 30 second exposures (total exposure 14m 00s)
Motion 2.6"/min in p.a. 216

All images binned 2x2 and enlarged x2. field 5'x5', North up
0.30m f/6.3 Schmidt-Cassegrain + CCD

Originally added to the NEO Confirmation Page with temporary designation AO19841 early on 30th May  2004 this object stayed on the page for 4 days. Often this is due to the Minor Planet Center waiting to see whether observers are going to report any cometary features on an object they suspect may be cometary. As soon as the first few positions had started to come through it was obvious to the MPC that the orbit was highly inclined and retrograde and likely to be a comet.

Images taken at Great Shefford on 2004 May 31.0 UT were initially examined on the night for cometary features and in a stack of the first set of 21 images it appeared slightly diffuse, enough for a second set to be obtained 1h 20m later. The second set appeared sharper and the positions were sent off without comment to the MPC soon after.

By the next day, as it became apparent the object was being left on the NEOCP longer than normal, I took another look at the images taken on May 31st and sent the following text off to the MPC on 1st June 2004:

'I have just re-examined images of AO19841 taken 2004 May 31 00:08 - 00:20 UT and May 31 01:40-01:53 UT and find that the object is significantly different in appearance to field stars of similar brightness, having a FWHM diameter at least 50% larger.

10 stars in the first set of exposures were measured to have a FWHM of between 4.6 and 6.2" (average 5.3") with the object measured to have a FWHM of 9.7".

10 stars from the second set (slightly better quality images) were measured to have a FWHM of 4.8 to 5.5" (average 5.2") with the object measured to have a FWHM of 7.9".

In a stack of 42 exposures (total exposure 15m 24s) the object appears to be of mag +18.8 with a diameter of 12" and a 3" diameter central condensation. There is just a hint of a 9" wide extension from the condensation in p.a. 90 degrees for approximately 20".'

The Central Bureau e-mailed CBET 68 (preliminary announcement of C/2004 K3) on 3rd June 2004 and later IAUC 8350 was issued on 11th June 2004 formally announcing the discovery.

Further images obtained June 7.0 and June 8.0 UT showed the object to be brightening and to have a short extension to the coma to the southwest and by June 28.0 UT this extension had swung around to the east (see animation above, which has the direction of the Sun marked with an S, the elongation of the coma can be seen to swing around opposing the solar direction).

If the comet had been following the brightness changes predicted by the ephemeris it would have faded by 1 magnitude from June 8th to June 28th, but in reality held its brightness, possibly brightening slightly.

The comet was not observable after June 28th from Great Shefford, setting behind the tree line to the North West while the summer sky was still too bright to image it.

This intrinsically faint comet was due at perihelion on June 30th 2004, at a distance of 1.1 AU from the Sun, but passed closest to Earth on June 1st at a distance of 0.58 AU. With an inclination of 112 and perihelion occurring soon after the comet passed its ascending node, it swiftly moved to high northerly declinations between June 9th and 25th (north of +69 and therefore not observable with the Meade telescope/Apogee camera combination at Great Shefford). 

The Minor Planet Center issued MPEC 2004-N12 on July 2nd using 72 positions from May 29 - June 30 2004, showing the comet with an elliptical orbit for the first time with a period of 446 years. A day later Syuichi Nakano issued a very similar elliptical orbit using the same observations and listing the period as 447 years.


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