2008 May notes: 2008 JL24

After a promising opening week, May turned out to be yet another disappointing month, with just a handful of (cloud interrupted) nights.

The most interesting object observed during the month was 2008 JL24, a mag +17.5 LINEAR discovery added to the NEO Confirmation Page (NEOCP) just before midnight on 11th May and predicted to be moving at about 25"/min. The sky cleared at Great Shefford a couple of hours later and I started searching for it at 00:25 UT. The uncertainty area indicated by the Minor Planet Center was about 80' wide, much bigger than my 18'x18' field of view. I started imaging at the nominal position, at the western end of the area and while the first set of images was being taken I checked with FindOrb whether by chance any of the astrometric positions submitted by LINEAR had poor residuals, in case I could possibly improve the prediction. All the positions looked good, but the ephemeris generated by FindOrb had the object way off to the east, beyond the furthest eastern extent of the NEOCP uncertainty area.

I decided to start searching from the FindOrb prediction and to work my way back to the western side of the NEOCP area with overlapping fields. I picked up the NEO in the corner of the second field attempted, over 1.5 degrees from the nominal position, but in fact only 10 minutes after I had started observing! I re-centred and obtained some further images and sent off the astrometry to the Minor Planet Center.

Initial uncertainty area for 2008 JL24.
White cross is MPC expected position, orange and red dots indicate MPC expected uncertainty area, yellow boxes are telescope fields originally planned to cover MPC uncertainty area.
4 coloured boxes on left show the search fields taken, with the actual position of 2008 JL24 marked with a red cross. Arrow length indicates the motion of the NEO in 1 hour.
Sky chart and field boxes plotted using SkyMap Pro 9.

When LINEAR discovered 2008 JL24 it was just inside the orbit of the Moon, at 0.94 Lunar Distances (LD) and by the time I confirmed it 18 hours later it had already receded to 1.4 LD. Over the years LINEAR has discovered a number of fast moving objects that were probably closer than the Moon at the time, but never picked up again and in fact 2008 JL24 is the first time that a NEO has been discovered while closer than the Moon and then subsequently confirmed. It was well observed over the next five days before fading out of sight just before the full Moon.



 

2008 April notes: 2008 GM2, 2008 GF1

After a good run of more than a week of clear nights in early April, the rest of the month brought rather poor weather, only a couple of nights in the month were were completely cloud free.

Two NEOs (both discovered during April with telescopes of the Catalina Sky Survey) came closer to Earth than the Moon, 2008 GM2 was discovered three days after its close pass, so had already receded to about 2.7 Lunar Distances (L.D.) before being picked up. I recorded it about 14 hours after discovery at about 3.3 L.D. but already it had slowed to a very sedate apparent speed of 6"/min.

The other was 2008 GF1, discovered on April 5th just over two days before closest approach and last caught from Great Shefford just before midnight, late on April 6th when it was moving at 70"/min and at mag +17.6, just over 2 L.D. away, about 12 hours before passing Earth at 0.8 L.D. Unfortunately, it was not picked up again, favourable locations for observing the fly-by being in central Asia, so both these NEOs went unobserved when at their closest.

2008 March notes: 2008 EZ7

Observing was limited in March, a combination of poor weather with very few nights keeping clear throughout and also the telescope being out of operation for a week, the problems eventually being tracked down to a failing mains transformer (see investigation in progress).

On 7th March (four days before the telescope broke down!) the Apollo 2008 EZ7 was discovered from the Siding Spring Observatory in Australia. From its accelerating motion it was obviously already very close to Earth and it was put on the NEO Confirmation page later that day. With a rapidly expanding uncertainty area where the new fast moving object was predicted to be I was fortunate enough to be able to confirm it later that evening at magnitude +17, at an altitude of less than 13 degrees, shortly before it disappeared into trees.

The next night it was to pass only 0.419 Lunar Distances (100,000 miles) from Earth, closest approach being at 01:21UT on 9th March. The first half of the night was cloudly but with breaks expected later in the morning. I started to try for it through gaps in the clouds at 01:47UT at which time it was moving at over 630"/minute. On the first low resolution shot taken to position the telescope, there it was, very obvious as a strong 30" long streak in the 3 second exposure. However, for the next half an hour the clouds stopped me getting anything other than more positioning shots, but eventually it was recorded in a 30 second gap in the clouds, enough to get eight 1 second exposures off. At that point it was magnitude +13, moving at 623"/minute and only about 102,000 miles from Earth.

The eight (rather noisy) images have been combined here with 2007 EZ7 moving from right to left. The field of view is 18'x18' and there is a 2 second gap between each of the exposures.

A few minutes later, when repositioning the telescope for the next attempt I recorded 2007 EZ7 streaking along as before, but also with another very similar streak in the field of view. This turned out to be artifical satellite 1985-048C=15825U, moving at about 900"/minute and more than four times closer than the NEO. I wonder how many NEOs on very close approaches are assumed to be artificial satellites in CCD images?

2007 EZ7 is to the right and 1985-048C is the slightly longer streak to the left below.

At the time of writing there have only been two other NEOs (with well determined orbits) that have been observed closer to Earth than 2007 EZ7, those being 2004 FH and 2006 DD1, but no doubt, with the pace of NEO discoveries at the moment, it is only a matter of time before another is seen to fly past even closer. Just three weeks later 2008 FP came closer than the Moon and was observed by the Catalina Sky Survey only slightly further out than 2007 EZ7, at a distance of 106,000 miles.

2008 January notes: 2005 BT1, BI10604, 2007 XS16, 2008 AV72 = 2000 JF4 = 2006 PH11

January was rather disappointing with fewer hours logged observing than for the same month in any of the previous 5 years.

A highlight was the recovery of the Apollo 2005 BT1, originally discovered by LINEAR on 16 Jan 2005 and followed for 47 days. Predicted to have a favourable approach in Jan 2008, a search was started from Great Shefford on Jan 24th, the expected magnitude given by the Minor Planet Center was +19.1 and the likely uncertainty area given as over 8 degrees long, aligned almost North-South.

I covered the central 4 degrees with my 18'x18' field of view during 24/25 Jan and extended this to the N by another degree on 26 Jan but searching was cut short by clouds. Only 0.5 degrees was added to the S the next night before clouds interrupted again, but finally on 28 Jan, on the first attempted field that night the NEO was finally caught, 2.35 degrees off track to the south. It had taken 814 images taken on the four nights, of 30 separate fields to locate it.

The next night was cloudy again in the UK so I contacted Sergio Foglia (IAU code 147) and Luca Buzzi (code 204) in Italy to see if either of them had good skies to try and get a confirming second night of positions for it. Sergio was not able to observe but Luca managed to get some astrometry before he too was clouded out. With the positions from 2008 Sergio then searched for possible images from the old SkyMorph image archives and managed to locate it faintly on two images from 07 Jan 2002 taken with the Palomar 1.2-m Schmidt. All three sets of positions were sent off to the MPC and within the hour MPEC 2008-B60 was issued formally announcing the recovery.

Another extensive search that didn't end up with such a positive result was also a LINEAR discovery found at 03h UT on 16 Jan and posted on the NEO Confirmation page with temporary designation BI10604 just after midnight on 17 Jan. Although relatively bright at mag +17, by the time I could observe on the evening of 17 Jan the uncertainty area was a 1 deg x 2.5 deg oval. I covered the whole area with multiple images being taken of 31 different fields, but did not find it. By the end of the 4 hour session the area had already expanded by a further 0.5 degrees. It never did get recovered by any observatory and two nights later was removed from the NEOCP...

A good set of luck came my way on 7th Jan while I was following up on one of the main belt discoveries I had made in December (2007 XS16). I found a very faint moving object, about mag +21, that did not match any known object and so measured positions of it. I had hoped to try for it again in the coming nights and send in two nights of astrometry to the Minor Planet Center, but clouds stopped any further attempt for over a week. By 17th Jan I decided to just send in the positions as a one night stand (ONS), expecting that I would not hear any more about it. However, by the next day the MPC had managed to match it up to a ONS from the 1.5-m reflector of the Mt Lemmon Survey obtained 5 days after mine on 12 Jan. It was designated as 2008 AV72 and I was given discovery credit for having the earlier of the two ONS!

With this extra data I now realised that other images taken of 2007 XS16 from the previous month might include 2008 AV72 and on re-examining these managed to find it on images taken 29 Dec and then 19 Dec 2007. After these pre-discovery positions were sent in, the MPC quickly managed to find various other ONS back to May 2000 and even two occasions where the object had been given a designation on the basis of two nights of observations (not enough to determine a proper orbit), these being 2000 JF4 and 2006 PH11. Because 2008 AV72 had a 2 month observed arc in 2007/8 it was retained as the primary designation and with observations at 5 oppositions and an MPC uncertainty code of 1 it is now in a state where it could potentially get numbered - not bad for just sending in the ONS from 07 Jan having lost hope of being able to find it again!

2007 December notes: Observing statistics, 2007 XZ9

2007 ended up with some surprising statistics for Great Shefford. Even though we suffered the very bad run of summer weather from May through August I ended up with about 5% more nights used than in 2006, about 5% more time exposing the CCD (22 days 3hours in total) and about 14% more images taken than in the previous year.

The Catalina NEO Survey was snowed out for some of the month, though for the remaining time there were still some fairly busy periods, with several occasions when there were 20, 30 or more newly discovered objects needing follow-up on the NEO Confirmation page. More than 50 new NEOs were eventually added by the surveys to the overall tally by month end, despite the weather.

One consequence of the surveys being out of action for days at a time was a good crop of main belt minor planets available for discovery by amateurs. I picked up 12, my highest monthly total and other amateurs were also very successful too. Most of the NEOs observed here were only picked up for one or two nights, with 2007 XZ9 (an Apollo discovered by LINEAR) being observed the longest, but that only for 6 days.