A decade of operations and a few close approachers

The end of May marked 10 years of operation at Great Shefford Observatory, first light occurring on 26 May 2002 with the first astrometry being  measured on 30 May 2002, of Comet C/2000 WM1 (LINEAR). In the intervening 10 years I've taken 831,500 images and measured 30,600 astrometric positions of minor planets and comets, with many of the images being taken for photometry rather than astrometry.

The weather in April and May this year was particularly poor and looking at the stats over the last 10 years, this April was the worst April in all that time, with only 11 nights usable, nearly half of what would normally be expected. Indeed the 18-night cloudy period from April 23 - May 10 was easily the longest endured here, the previous worst being a period of 12 consecutive cloudy nights in January 2011.

In what remained of the month there were a number of notable close approachers observed, first up was 2012 JU, discovered at 6am UT on May 12th by the Catalina Sky Survey, 31 hours before passing by at 0.53 Lunar Distances (LD). David Briggs at South Observatory, Clanfield (code J84) reported positions during the evening of the 12th at mag +17 and I first picked it up at 23:15 UT, following it for just over 2 hours. In the 3 hours that David and I had it under observation its distance from Earth decreased by 1/5th, to 1.6 LD and its apparent speed accelerated from 60"/min to 90"/min. It was last reported from the Astronomical Research Observatory, Westfield, USA (observatory code H21) at 6h UT on 13th at 1.04 LD, moving at 208"/min at mag +16.

A much better observed fly-by was 2012 KP24, discovered from Mt. Lemmon with the 1.5-m reflector on May 23rd, giving NEO observers the luxury of 5 days warning before closest approach, due at 15:21 UT on May 28th, just 4 Earth diameters from the Earth's surface! At discovery it was mag +21 and 15 LD from Earth. I observed it on four consecutive nights, initially moving at just 1"/min and at mag +20 on May 24/25 but brightening about a magnitude each night. My last measurement was mag +16 in strong twilight at 02:40 UT on May 28th, with it still only moving at 30"/min even though by then it was only 1.5 LD away. It was last reported at 10:24 UT that morning, by the Catalina Sky Survey at mag +14 and moving at 187"/min, 5 hours before closest approach. Sergio Foglia posted on the Minor planet Mailing list a lightcurve derived from observations from H21 that shows a rotation period of 150 seconds and an amplitude of about 1 magnitude for this object, estimated to have a diameter between 13-19 metres.

However, even before 2012 KP24 was out of the way, the Mt. Lemmon telescope had picked up the next incoming object, 2012 KT42. The discovery image was taken just 23h 58m before 2012 KT42 would skim the Earth's surface by a mere 1.1 Earth diameters. As with 2012 KP24 the timing of the close approach would favour observatories in the USA more than those in the UK, with closest approach at 07:07 UT on May 29.

At discovery 2012 KT42 was at 3.6 LD and within 1.3° of the opposition point, about midway between Antares and Beta Sco and headed almost exactly towards Earth. From Great Shefford it was low in the south that night and I had to wait for it to pass into gaps between trees but eventually managed to image it for a 13 minute period a few minutes after midnight early on May 29th and again from 01:17-02:05 UT. It was mag +15 but only at 13° altitude by 2am.

2012 KT42, mag. +15.5, moving 49"/min, Distance from Earth 0.8 LD
Stack of 77 x 4 second exposures, 01:31:30 - 01:45:56 UT 29 May 2012
0.40-m Schmidt-Cassegrain at f/6, 2.1"/pixel, field 9.4'x7.7', North up.

Even though it was nearly 19 hours after discovery it had only moved about 3° from the discovery position, still headed almost straight at us, but had approached to just 0.76 LD by then. Mt. Lemmon remarkably managed to keep it under observation to within an hour of closest approach, their last reported astrometry was at 06:17 UT when 2012 KT42 would have been about 12th mag and just 3.6 Earth diameters above the Earth's surface, screaming along at 1,630"/min, equivalent to the apparent diameter of the moon in less than 70 seconds!

The alignment of 2012 KT42 during this approach was quite interesting, as already mentioned, it was nearly at the opposition point during most of the approach, but was actually in the Earth's penumbra from about 14:10 to 21:40 UT on May 28th. After close approach the line-up was still perfect and 2012 KT42 was in transit in front of the Sun for about an hour either side of 10:12 UT on May 29th, though far too small at about 0.006" diameter to be visible from Earth.

2009 December notes: 2009 WZ104, 9U01FF6, 2009 observing statistics

December provided a reasonable amount of observing time but the number of NEOs discovered by the surveys was much reduced, 34 new objects compared to the 116 they picked up in November, so NEO follow-up work was quieter than of late.

As well as following objects on the NEO Confirmation page, the opportunity was taken to follow 2009 WZ104 on several nights to try and determine its light curve. This is an Aten discovered on Nov. 25 by the Catalina Sky Survey and was brighter than 17th mag. for the first two weeks in December. However, not enough coverage was obtained to be able to find an unambiguous period, but it is likely to be longer than 6-8 hours.

The unusual artificial satellite 9U01FF6 mentioned last month in TA Vol 46 No 548 p211 (2009) which is in a 30+ day, very elongated orbit, taking it as close to us as 5 Earth diameters and about twice as far as the Moon at apogee, was picked up again on Dec. 27, three days before perigee. It was only 5" from the prediction calculated with FindOrb using positions from the previous two returns and taking into account Solar Radiation Pressure. Unfortunately the weather stopped any further observations but it should be visible next on the night of 6th Feb. 2010 and then in March a relatively long apparition, from the 11th-15th.

2009 overall was an exceptionally good year for observing at Great Shefford, producing the best observing figures since my observatory was commissioned in May 2002. Several statistics follow, with the previous best figures and year in parentheses: The most nights used (202 vs. 183 in 2003), the most hours spent at the telescope (938h vs. 838h in 2005), the largest amount of time the CCD shutter was open (24d 00h vs. 22d 03h in 2007) and far and away the largest number of images taken in a year (148,361 vs. 92,025 in 2007). That last statistic is in part to do with more Minor Planet photometry being done in 2009 than before, with many objects being followed for long periods of time, collecting many images during a night. The total number of images taken since 2002 passed the 1/2 million mark during the year and now stands at 570,575.

2009 generally seems to have beaten my previous records by 8-12% all round. Lets hope 2010 doesn't let us down!

2009 June notes: Observing statistics, 2009 KL8, 2009 MU, 2001 FE90

2009 has provided some exceptional statistics for Great Shefford so far, more usable nights (103) & more hours used (455) in the first 6 months of the year since the observatory was commissioned in 2002, beating the previous best Jan-June (2005) by 10%. Hopefully the last half of the year will be equally good.

June started with the close fly-by of Apollo 2009 KL8, passing Earth at 5 Lunar Distances (LD) on June 2nd. That night it was moving at 60"/min and fading fast, from 19th to 20th mag. during the course of the night. Two nights before, even though about 30% further away it was about 1.5 magnitudes brighter because of its smaller phase angle and I followed it that night for 1h 45 minutes to try and determine its rotation period. That turned out to be just 2 mins 41 seconds, varying by 0.75 magnitudes and it had managed to complete 32 rotations while I was observing it!

Another close approach occurred on June 24 at 16:50 UT when 2009 MU passed at 2.3 LD. The night before it had been well placed throughout the few dark hours available from the UK and was followed at mag. +16, its speed accelerating beyond 100"/min by dawn. Initial indications are that its lightcurve is irregular, suggesting that it may be tumbling, but further analysis needs to be completed.

The Apollo 2001 FE90 was also observed towards the end of the month. Discovered in 2001 when it reached 18th magnitude, this year it was predicted to brighten to mag. +13.3 as it sped from north to south in the evening sky and was scheduled to be a RADAR target at Goldstone and Arecibo at the end of June. I first observed it briefly following a thunderstorm just after midnight on 26th June and in the 22 minutes before it was obscured behind trees it showed a dramatic variation of over two magnitudes in brightness! I observed it on the three following nights and watched the amplitude reduce to 1 magnitude as the phase angle reduced from 79° to 34°.

The lightcurve derived from about 30 minutes of images taken on the evening of 27 June 2009 is shown, including a mosaic of the images from the same sessions, showing the rise and fall in brightness of the Minor Planet as it trailed (from left to right). As can be seen, the observations cover just a couple of minutes less than one full rotation period.

2001 FE90 - light variations on 27 June 2009

2008 October: Observing statistics, 2008 UL90, 2008 UT95, 2008 TT26, 2008 TC26, 2008 TQ10, 2008 TR10, 2008 UX202

After months of disappointing weather throughout the summer at Great Shefford, October proved to be exceptionally good, with the largest number of hours (125h) recorded at the telescope in a single month since I commissioned the observatory in 2002.

The big news early in the month was the brief appearance of 2008 TC3, hours before impacting Earth early on Oct 7th. However, there were plenty of other new objects discovered by the surveys during the month, with over 50 being observed after having been put on the NEO Confirmation Page (NEOCP) by the Minor Planet Center.

One of the more interesting objects was 2008 UL90, a member of the rare Interior Earth Objects, or so called Apohele class, with orbits entirely inside the orbit of the Earth. There are only 14 definite or suspected members of this class to date. This one was at 66 degrees elongation in the morning sky when observed. It should brighten slightly to about mag +19.7 and the elongation increase by just a couple of degrees by mid-November before it slips back into the glare of the Sun during December.

A few fast movers were also followed, 2008 UT95 was last caught moving at 40"/min, just over 4 Lunar Distances (LD) from Earth on the night of Oct 31/Nov 1st, two days before passing Earth at 1.5 LD, but it was not reported from any observatory after Nov 1st. 2008 TT26 was well observed from a number of observatories during October and briefly reached mag +14 around Oct 22/23 when it was recorded moving at about 50"/min, at a distance of about 3.5 LD.

The good weather brought another record for me, a total of 12 new minor planets discovered during the month, with 9 of them found in the field of NEOCP objects. One, 2008 TC26, turned out to be a Hungaria class object, with an orbit inside the main belt, just further out than Mars and was found in the same field of view as two(!) NEOCP objects, 2008 TQ10 and 2008 TR10. The last of the new objects found was 2008 UX202 on 28 Oct and confirmed 3 nights later. This turned out to have a perihelion distance of 1.68 A.U., just outside the aphelion distance of Mars and like 2008 TC26 is in the inner zone of the main belt.

2008 August notes: Observing statistics, 2004 SB56, 2007 RT12, 2001 QL153, 2008 PG1

The weather was very poor at Great Shefford in July and August. With 25 hours at the telescope, July provided less than half the observing hours logged for that month in any of the last three years. August was officially the cloudiest August in the UK since records began in 1929 and provided only about 50 (generally poor quality) hours, again well below totals from recent years.

However, the night of August 3/4th provided the opportunity to recover three NEOs not seen since their discovery apparitions and a somewhat unusual confirmation of a NEO Confirmation Page (NEOCP) object.

Aten 2004 SB56 had sped northwards after conjunction with the Sun in July and in the 10 days before recovery had brightened 3 magnitudes and increased elongation from 35 to 72°. With an uncertainty area on the sky of 14' it was picked up only 3' from prediction at mag +16.7 and about 6° from the North Pole, a relatively easy recovery.

Apollo 2007 RT12 had an uncertainty of about 1° and at mag +20.0 was a potentially difficult object to recover, just 1° east of Alpha Cep, deep in the Milky Way. Fortunately it was only 8' from prediction and not involved with any field stars during the time it was imaged. With an absolute magnitude of +23.9, equating to an estimated diameter of 30-95 meters, there have only been 10 other NEOs recovered at a second opposition that are smaller than 2007 RT12. Included in this set are the Earth co-orbital companion 2002 AA29 and the tiny 2006 RH120 that was temporarily captured in Earth orbit during 2006 & 2007. My thanks to Sergio Foglia for providing a list of small NEOs seen at more than one apparition.

The third object was 2001 QL153, an Amor that had been observed for about 4 months and had not been seen since January 2002. It too had an uncertainty of about 1° and predicted to be mag +20.5 and could have posed a problem to pick up. It was in a less crowded field than 2007 RT12 and after more than six years since last being observed was recovered only 9' from prediction.

A LINEAR discovery put on the NEOCP on August 3rd turned out to be something of a puzzle. 2008 PG1 was observed from 9-10am UT on August 3 by LINEAR at mag +19, moving at 9"/min from west to east, in the morning sky about 13° north of Mira Ceti. By 2am on August 4th it was predicted to be accelerating and to have an uncertainty area 1.7° long, extending roughly West to East, in the direction of motion. I eventually confirmed it 43' further west than the most westerly point of the uncertainty area (quite unusual for the MPC prediction to be this far out) and moving at about the same speed as when LINEAR discovered it. The orbit appears to be rather indeterminate but it was announced on MPEC 2008-P14 with just the observations from LINEAR and my set of confirmation positions. The orbital eccentricity had been assumed (done sometimes when the orbit is rather indeterminate, to try and help improve the orbit solution). No other observatories had reported positions for the NEO before I got my next chance to observe the area early on August 9th. By then, using FindOrb software from Bill Gray to generate a large number of 'Monte Carlo' orbits to estimate the likely uncertainty area, it looks like it could have been anywhere in a nearly 3° long band. I didn't manage to locate it that morning nor on my next opportunity 4 days later and it has not been reported from anywhere else since. It is now listed as a Virtual Impactor by JPL with 97 potential impacts, the first in only 5 years time, but with such large uncertainties in its orbital elements the chance of collision then is given as just 1 in 200 million!

(Update 10 May 2012: 2008 PG1 was linked to 2009 EV by the Minor Planet Center, read more here)

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.

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.