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2006 CJ (Recovery at 2nd opposition)

2006 CJ was discovered on 1st Feb 2006 by Gordon Garradd at the Siding Spring Observatory, at that time it was 20th magnitude and at a declination of -21. Over the next few weeks it brightened to +18th mag, but remained at southerly declinations and was followed on another six nights, being last reported on 14th Mar 2006.

It travels in a very elongated orbit taking it to within 0.17 AU of the Sun at perihelion and just outside the Earth's orbit at 1.19 AU at aphelion. With a period of just 6 months, its orbit is smaller than the Earth's and is therefore classed as an Aten type object. At discovery it was just approaching aphelion, so was well placed in a dark sky.

From the 7 week span of observations made at discovery, it was predicted to make a close approach to the Earth around 1st Feb 2007. Having passed through perihelion in early Dec 2006, by Feb 2007 it was crossing the Earth's orbit, moving out towards aphelion at the end of Mar 2007.

Hidden by the Sun's glare until just a few days from closest approach on 1st Feb 2007 it would be heading swiftly north but it would only be visible from Great Shefford 2 days later and by that time the uncertainty in its position would be about 1 with the object anywhere on a line slightly South of East of the predicted place or slightly North of West. At a predicted magnitude of about +16 and moving at 23"/min (or the apparent diameter of the Moon in less than 1 hours) it would be an easy object to search for and recover.

In an effort to recover 2006 CJ, images were taken on the evening of 3rd Feb 2007, starting at the nominal predicted place. The field of view of the equipment at Great Shefford is about 18'x18' and the object was not seen in those first images. Further fields towards the East were then taken, with a 3' overlap, covering about half the uncertainty area to the East but the object was not found. Fields to the West were then taken and the object was recognised as soon as the first of these westerly fields were being exposed

The animation below shows the fields taken during the search and covers about half of the expected uncertainty area.

With an orbital period of 0.5562 years, 2006 CJ makes almost exactly 9 revolutions of the Sun in the time it takes the Earth to make 5 revolutions and so in 2011 and 2012 the circumstances almost exactly match those in 2006 and 2007, with a favourable aphelic opposition in Feb 2011 and a close approach around 1st Feb 2012, though not quite so favourable as in 2007.


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