[BAA 00300] Rare Appulse of Two Comets on July 20

[Rick]

BAA electronic bulletin No. 00300 - http://www.britastro.org/

Rare Appulse of Two Comets on July 20

Within the last day or so, three observatories have independently recovered periodic comet, P/2002 O5 (NEAT) - also known as P/2007 N2 (NEAT) and 189P.  The comet is currently passing about 0.2 AU from the Earth and is magnitude 15-16 and has a coma/tail about 20-25 arcsec across.

Seiichi Yoshida has just drawn attention to the fact that this comet will pass almost directly in front of another comet, C/2005 L3 (McNaught) on July 20 at about 22h UT.  This comet is very much further away being around 5 AU from the Earth and almost 6 AU from the Sun at present yet is slightly brighter than P/2007 N2 possibly magnitude 14-15.

Observers in the UK and Europe will have an opportunity to monitor this close appulse on the night of Friday 20th.  Seen from the UK, closest approach is at 22:03 UT (11.03 pm local time) when the cometary nuclei will be a mere 28 arcsec apart (less than the apparent diameter of Jupiter). Indeed the coma of both comets will overlap for a time.  Closest approach takes place about 10 minutes after the end of nautical twilight in the UK and so the sky will only just be dark enough to witness this very rare appulse.  The two comets will be fairly high in the sky (roughly 35 degrees altitude) seen from the UK and will be close to due south at the time.  The relative motion of the two comets is such that the faster-moving newly-recovered comet P/2007 N2 will drift past C/2005 L3 at an apparent rate of 5 arcsec/minute in position angle 030 degrees.

This is a real observing challenge for BAA members equipped with a CCD camera and a moderately large telescope.

The mid-position at closest approach, which is in the constellation of Ophiuchus, will be:

R.A. 17h 21m 31.5s
Dec.-01d 59m 20s

Richard Miles

[Rick]

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