2007 March notes: 2007 EH, 2007 EK and 6R10DB9

March was an exceptional month for NEO close approaches, with ten objects observed moving faster than 25"/min, and two observed while inside the distance of the Moon.

In the table below "/min is the apparent speed of the object in arcsec/minute and LD = Lunar distance = 0.00257 AU

Object	March UT	"/min	Distance AU	Distance LD
2007 DJ	01.9	30	0.021	8
2007 DX40	02.1	33	0.028	11
2007 EH	11.1	1,250	0.0011	0.4
2007 EK	13.2	382	0.0018	0.7
2007 EV	15.2	42	0.016	6
2007 EO88	18.8	288	0.0032	1.2
2007 FC3	20.8	142	0.0090	3.5
2007 FG1	22.0	25	0.025	10
2007 FY20	31.9	35	0.018	7
2006 VV2	31.9	57	0.024	9

2007 EH is the fastest natural object I have tracked and is currently the third closest observed approach of a designated minor planet ever (only 2004 FH and 2006 DD1 having had astrometry reported while closer).

It was discovered 44 hours before the close approach and put on the NEO Confirmation page during the afternoon of 9th March, but that evening, with it still unconfirmed I spent some time searching about +/- 0.5 degree around the predicted position but without success. Reviewing the discovery positions from the Catalina Sky Survey, one or two looked somewhat out of step with the others and so an orbit was calculated leaving these out. The resulting prediction was about 1 degree west of the NEOCP prediction and the object was indeed picked up close to that place, allowing the subsequent close approach prediction for the next night to be greatly refined.

The close approach itself was remarkable, to watch images appear on the monitor with the object racing across so fast... at it's fastest speed of 1,250"/min it was 15th mag and covering the field of view of my CCD in 53 seconds, or the diameter of the Moon in less than 1.5 minutes! When first picked up on the evening of the 10th at 19:16 UT it was at RA=11h 41m Dec=+30, reached RA=15h 50m Dec=+60 at 00:45UT on 11th and was last seen at 02:22UT at RA=19h 37m Dec=+50, over 80 degrees of sky covered in less than 7 hours!

Full details of the confirmation, animations from the close approach night and details of the techniques used to measure astrometry of such a fast moving object can be found at http://www.birtwhistle.org/Gallery2007EH.htm.

2007 EK which passed at 0.7 Lunar Distances just two nights after 2007 EH would in a more average month have headlined itself. However, it was nearly two magnitudes fainter than 2007 EH and so was not quite the spectacle of the earlier NEO.

One other noteworthy object seen during the month was 6R10DB9, a Catalina Sky Survey temporary designation given to an object discovered last September which has since then been in geocentric orbit, originally expected to be a small piece of man-made space junk, but increasingly suspected of being natural. It was picked up at mag +19 moving at 24"/min in a dense starfield in Gemini, just 1.2 Lunar Distances from Earth, as it approached it's 2nd to last perigee. It will be perturbed out of the Earth's vicinity for the foreseeable future this coming summer. Attempts to obtain spectra with the 6.5-m MMT during the March perigee were unfortunately clouded out, but there will be one last opportunity in June to try and determine once and for all whether it is indeed a natural object. Some details of the story so far of this interesting object can be found at http://www.birtwhistle.org/Gallery6R10DB9.htm, but hopefully more to come in June and July.

2007 February notes: 2007 BD7, 2007 BZ48 and 2007 DA61

The first half of February was reasonably favourable with 8 nights used up to the 14th and 49 hours logged, while the last half of the month was very poor, with just 4 cloud interrupted hours logged over 3 nights.

Apollo object 2007 BD7 discovered on 23 Jan 2007 from Lowell was followed on four nights up to 6th Feb as it approached Earth, with it's phase angle reaching about 90 degrees on the last night. It was moving swiftly into evening twilight and with the phase angle continuing to increase and magnitude fading rapidly it was not seen again.

Another Apollo 2007 BZ48, discovered by the Mt. Lemmon Survey in January and making a close approach in February, was also observed on four nights, last seen on the morning of the 7th within hours of it passing Earth at 4.5 Lunar distances at a moderately fast 56"/minute.

The only object imaged from the NEO Confirmation Page in the last half of the month was 2007 DA61, during a half hour gap in the clouds on 25th Feb. This turned out to have a perihelion distance of 2.6 AU, in a highly elliptical orbit, elements available by early March giving P=134 years and indicating perihelion at the beginning of March 2007 (though these values may change somewhat as further positions are obtained). It appeared completely stellar in my images and is likely to be a Damocloid asteroid, but it is possible it might show some signs of outgassing with large instruments in the coming weeks.

2007 January notes: 2007 AG2 = 2004 BO41, 2007 BD

A LINEAR discovery added to the NEO Confirmation page on 8th Jan was eventually confirmed from Great Shefford 2 days later at +69 degrees declination in the evening sky and followed for four nights over the next two weeks at magnitude +18/19. Given the designation 2007 AG2, it was strangely not followed up by any other observatories. Then on 25th Jan I heard from Sergio Foglia that he had identified 2007 AG2 with the NEO 2004 BO41 which had been discovered by LINEAR and observed from 19-29 Jan 2004 and co-incidentally I had observed on several dates that apparition as a morning object, eventually being lost in the twilight.

I had searched for 2004 BO41 a year after discovery on 3rd Jan 2005, covering about 1 degree of sky. It turns out that the actual position at that time was more than 12 degrees further on, so even 12 months after discovery it was hopelessly lost and by Jan 2007 was many tens of degrees off track.

Another interesting object this month, 2007 BD was discovered by Eric Christensen at the Catalina Sky Survey using the 0.68-m Schmidt. It was only 3 Lunar Distances away and already 17th mag, moving at 27"/min. It passed inside the Moons orbit 32 hours later, reaching a minimum distance from Earth of 0.84 L.D. on 18 Jan 2007 at 02:53UT and was well observed from the Crimea-Nauchnij, Gnosca and Modra observatories and also from the Catalina Sky Survey during the 16 hours it remained inside the Moons orbit. It was last caught from Modra 42 minutes before closest approach, travelling at 303"/min at mag +13.
It was then picked up again from Catalina 52 minutes after closest approach.

Unfortunately, during the close approach I was clouded out, but did manage to catch it 2 nights later when it was still about mag +19 and moving at 11"/min. This is quite unusual to be visible for several days on each side of an approach within the orbit of the Moon. It turns out that 2007 BD is an Aten minor planet with an orbit smaller than the Earth's, taking just 230 days to circle the Sun and with an aphelion distance of 0.986 AU it could be argued to be an Apohele (orbit being entirely inside that of the Earth). However, with the Earth at perihelion in January and the object reaching aphelion literally on the day of close approach, it was overtaken by Earth, passing just 200,000 miles outside the Earths orbit, appearing to approach from almost due East and to recede due West so was therefore almost equally well placed for observers for days either side of close approach.

2006 December notes: Observing statistics

After a very good November, the weather in December was much poorer. Only ten nights were usable with several of those being near the Full Moon. Ten consecutive cloudy nights over the Christmas break was the longest cloudy period at Great Shefford since the start of 2004. 14 objects were observed off the NEO confirmation page, along with another 15 NEOs, all but a couple were observed just on single nights.

Stats for 2006 (2005) show a slight reduction in clear nights from the previous year, but an increase in the number of images taken, due mainly to the upgrading of the CCD in Sep 2005 to allow faster image download times. Images were taken on 169 (181) nights, while the number of hours spent observing was 798 (841). However, 80,515 (69,239) images were taken, with the CCD shutter being open for a total of 507 hours (438 hours) over the year.

2006 November notes: 2006 WV

November ended up providing the most observing time at Great Shefford since Nov 2005, 105 hours over 16 nights.

The NEO highlight of the month was 2006 WV, discovered on Nov 17th with the 0.68-m Schmidt at Catalina. At 20th mag and moving at a moderate 2"/min at discovery it was added to the NEO confirmation page and was searched for on the evening of Nov 18, but not found. Unusually it was outside the uncertainty area predicted by the Minor Planet Center, reason being that it had unusual motion because it was headed almost directly for us and was accelerating rapidly towards a very close encounter at 10am on 21 Nov, within the orbit of the Moon.

LINEAR and the Mt. Lemmon telescope of the Catalina Survey picked it up again less than 24 hours later and it was observed from Great Shefford on Nov 19.0 UT, moving at 6"/min and at mag +19. The next night was cloudy, but by 9pm on 20th Nov it had brightened up to mag +16.5 and was racing along at 150"/min! By this time it was about double the distance of the moon and closing fast. It was followed on and off all night, finally lost to the morning twilight at 6:47am on 21 Nov with the Sun just 7 degrees below the horizon, by which time it was moving at 414"/min (or the apparent diameter of the moon in about 4 minutes), mag +15 and just at the point of crossing inside the moons orbit. Although not reported again, closest approach was 3 hours later at a distance of 349,900 Km (0.91 Lunar distances).