Although many nights in November had interruptions from cloud, observing time was logged on 18 nights and there were plenty of Near Earth Objects to be followed that had been discovered during the month by the surveys.
Apollo 2009 VX had been discovered on Nov. 9th by the Catalina Sky Survey (CSS) as a 19th mag. object but had brightened to 17th mag. by the time it was picked up from Great Shefford early on the morning of Nov 12th, moving at 150"/min. It was then at 2.8 Lunar Distances (LD) and would pass at 2.59 LD at 13h UT the same day.
Another relatively bright new discovery was Apollo 2009 VZ and although it didn't get any closer than 15 LD it remained above 17th magnitude for 12 nights, I recorded it at 15th mag. on Nov. 12 & 14th. 2009 VZ was intrinsically about 5 magnitudes brighter than 2009 VX, which translates to 2009 VZ having a diameter about ten-times larger than 2009 VX (approx. 300 meters vs. 30 meters), assuming similar albedos for the two objects.
2009 WJ6 was another CSS discovery from Nov 19th and was followed from Great Shefford later that same day. By then it was already about mag. +17.0, at 2.1 LD and moving at 58"/min. It reached its closest to Earth at 11am UT the next day at 0.46 LD and was reported from the Westfield site of the Astronomical Research Observatory, Illinois three hours before perigee, at a distance of 0.82 LD.
One other close approach Apollo object was 2009 WV51. Discovered at 7am on Nov 23 by the CSS it was due to pass at just 0.39 LD the next day. I picked it up on the evening of Nov 23 at 17th magnitude when it was at a distance of 2.8 LD and moving at 'just' 22"/min. Watching individual images download it was easy to see it rising and falling in brightness by approximately 1 magnitude in just a few minutes, though the lightcurve has yet to be reduced. It was last reported from the Magdalena Ridge Observatory, New Mexico on Nov. 24 at 05:43 UT with the 2.4-m reflector, at a range of about 1.8 LD. It went unobserved from Great Shefford that night at its closest approach due to bad weather, but would have been 14th magnitude and moving at over 1,000"/min in the early evening of Nov. 24.
The probable artificial satellite 9U01FF6 mentioned last month was due back at perigee early on Nov. 28 after being followed for only 44 hours by 7 observatories at the end of October. I started searching for it on the evening of Nov 23 but given a likely positional uncertainty of up to 1°, the waxing Moon only about 30° to the south and the predicted mag. being +21.2 I was not expecting much success. However, it was picked up only 5' from the predicted position and ranging in magnitude from +20.5 up to +18.9, the standard asteroid magnitude formula obviously not providing a good fit for this object! Further positions obtained on three subsequent nights allowed the effect of Solar Radiation Pressure (SRP) to be determined using FindOrb using all the available observations (26 October - 27 November 2009). SRP effectively pushes an object away from the Sun and the smaller the mass and larger the surface area of the object exposed to the Sun, the larger the discrepancy from Newtonian motion may be observed. Without taking into account SRP the RMS residual for 78 positions over the two apparitions is a very unsatisfactory 16", but taking into account SRP this drops to 0.8". The value of SRP (or Area/Mass Ratio) determined was 0.011 m2/kg which is similar to those determined using FindOrb for other distant artificial satellites, e.g.
LCROSS (incl. Centaur) size 14.5m x 4.7m, mass ~3,200kg, SRP = 0.015 m2/kg
IMP8 size 1.4m x 1.6m, mass 371kg, SRP = 0.010 m2/kg
ASTRON (1983-020A) size 6m long, mass 3250kg, SRP = 0.008 m2/kg
and is 10 times larger than the 0.0011 m2/kg value derived for 2006 RH120 (=6R10DB9), the tiny (natural) minor planet that was temporarily trapped in Earth orbit during 2006-2007. All this points to 9U01FF6 being man-made and from a posting on the SeeSat-L (Visual Satellite Observers) mailing list here http://www.satobs.org/seesat/Oct-2009/0176.html it is suggested that 9U01FF6 is very likely to be from a lunar transfer mission of some kind, but the perturbations on the orbit make identification of the specific launch very difficult. It is noted that some of the Agena rockets for the Ranger missions of the 1960s were in very similar orbits.
Sunday, 6 December 2009
Saturday, 31 October 2009
2009 October notes: 2009 TM8, 2009 UD, 2009 UV18, LCROSS and 9U01FF6
Apollo 2009 TM8 made a very close approach to the Earth early on Oct. 17th about 48 hours after discovery by the Catalina Sky Survey. It was followed from Great Shefford from soon after sunset on Oct. 16th when it was moving at an apparent speed of 180"/min, through to 04:20 UT the next morning by which time it had accelerated to 285"/min. It reached its closest to Earth at 03:37 UT at a distance of 0.9 LD. The brightness stayed fairly constant, around mag. +17.5 all night, the decreasing distance from Earth being offset by increasing phase angle but the large increase in apparent speed made it a more difficult target as the night wore on.
Another newly discovered Apollo, 2009 UD passed Earth at 2 LD on Oct. 20 and was observed on the morning of Oct. 17th for 2 hours and again for 3 hours the next morning when it was at about 3 LD and mag +17.0. Over 1,000 images were obtained in those 5 hours and allowed the determination that this ~15 metre diameter object rotates very fast with a period of 83.7 seconds with an amplitude of about 0.7 magnitudes.
2009 UV18 was an interesting LINEAR discovery from Oct. 22, relatively bright at mag. +18 and unusually large for a new discovery, estimated at over 2 km diameter. With a low inclination and the Earth approaching the ascending node of the orbit the size of the orbit was initially rather indeterminate and attempts at trying to identify it with a known minor planet failed, even though it ought to have been relatively bright in earlier apparitions. Then, on Oct. 29, Rob Matson, well known for precovery work with online image databases managed to find it on old NEAT images from Jan 2004, fortunately only 2.5° from the predicted place, even though the uncertainty was estimated at up to 90°.
The orbit of 2009 UV18 is similar to a Jupiter family comet and although it appeared stellar in images taken on Oct.23 and Oct. 26th it is probably worth keeping an eye on as it approaches perihelion this January in the morning sky. The last favourable return appears to have been in May 1993 when it should have reached mag. +16 and before that spring 1976 at mag +17.
The LCROSS mission was followed one final time on the night of Oct 8/9th. The spacecraft was only 6.4° from the gibbous Moon and internal reflections in the telescope made it a difficult target. Unfortunately the sky clouded over before the LCROSS shepherding spacecraft separated from the Centaur at 02:50 UT, the last images obtained that show LCROSS were taken at 01:56 UT but were so light polluted they could not be measured. The image of LCROSS was taken about an hour earlier, before the glare from the Moon became too strong, less than 11 hours before impact with the Moon.
What initially appeared to be a Near Earth Asteroid discovery was reported by the Catalina Sky Survey on Oct 26 and received their temporary designation 9U01FF6. It was 19th magnitude and moving at 10"/min but was already closer to Earth than the Moon. After follow-up from other observatories that same day it was found to be in a very unusual 31.5 day period, highly eccentric geocentric orbit, taking it to within 82,000 km of Earth (0.2 Lunar Distances) at perigee and out to 761,000 km (2.0 LD) at apogee. With an absolute magnitude of +30.9 it would only be 1-2 metres in diameter if it were a natural object, but smaller if artificial (with a higher albedo assumed). Further observations were made from Great Shefford on the evening of Oct. 27th and the last positions reported this perigee came from the OAM Observatory at La Sagra in Spain early on Oct. 28th.
9U01FF6 is fainter than mag. +21 for most of its orbit but will next be at perigee around Nov. 28th and should reach +16th magnitude but moving as fast as 250"-500"/min on the evening of Nov. 27th. Hopefully it will be recovered in the days leading up to that but observability is probably limited at most to only 2-4 nights each perigee. It is likely to be an unusual artificial satellite but further observations at the end of November are encouraged.
Another newly discovered Apollo, 2009 UD passed Earth at 2 LD on Oct. 20 and was observed on the morning of Oct. 17th for 2 hours and again for 3 hours the next morning when it was at about 3 LD and mag +17.0. Over 1,000 images were obtained in those 5 hours and allowed the determination that this ~15 metre diameter object rotates very fast with a period of 83.7 seconds with an amplitude of about 0.7 magnitudes.
2009 UV18 was an interesting LINEAR discovery from Oct. 22, relatively bright at mag. +18 and unusually large for a new discovery, estimated at over 2 km diameter. With a low inclination and the Earth approaching the ascending node of the orbit the size of the orbit was initially rather indeterminate and attempts at trying to identify it with a known minor planet failed, even though it ought to have been relatively bright in earlier apparitions. Then, on Oct. 29, Rob Matson, well known for precovery work with online image databases managed to find it on old NEAT images from Jan 2004, fortunately only 2.5° from the predicted place, even though the uncertainty was estimated at up to 90°.
The orbit of 2009 UV18 is similar to a Jupiter family comet and although it appeared stellar in images taken on Oct.23 and Oct. 26th it is probably worth keeping an eye on as it approaches perihelion this January in the morning sky. The last favourable return appears to have been in May 1993 when it should have reached mag. +16 and before that spring 1976 at mag +17.
The LCROSS mission was followed one final time on the night of Oct 8/9th. The spacecraft was only 6.4° from the gibbous Moon and internal reflections in the telescope made it a difficult target. Unfortunately the sky clouded over before the LCROSS shepherding spacecraft separated from the Centaur at 02:50 UT, the last images obtained that show LCROSS were taken at 01:56 UT but were so light polluted they could not be measured. The image of LCROSS was taken about an hour earlier, before the glare from the Moon became too strong, less than 11 hours before impact with the Moon.
What initially appeared to be a Near Earth Asteroid discovery was reported by the Catalina Sky Survey on Oct 26 and received their temporary designation 9U01FF6. It was 19th magnitude and moving at 10"/min but was already closer to Earth than the Moon. After follow-up from other observatories that same day it was found to be in a very unusual 31.5 day period, highly eccentric geocentric orbit, taking it to within 82,000 km of Earth (0.2 Lunar Distances) at perigee and out to 761,000 km (2.0 LD) at apogee. With an absolute magnitude of +30.9 it would only be 1-2 metres in diameter if it were a natural object, but smaller if artificial (with a higher albedo assumed). Further observations were made from Great Shefford on the evening of Oct. 27th and the last positions reported this perigee came from the OAM Observatory at La Sagra in Spain early on Oct. 28th.
9U01FF6 is fainter than mag. +21 for most of its orbit but will next be at perigee around Nov. 28th and should reach +16th magnitude but moving as fast as 250"-500"/min on the evening of Nov. 27th. Hopefully it will be recovered in the days leading up to that but observability is probably limited at most to only 2-4 nights each perigee. It is likely to be an unusual artificial satellite but further observations at the end of November are encouraged.
Sunday, 11 October 2009
2009 September notes: 2009 SH2, 2009 SN103, 2009 SU104, LCROSS and Herschel
September was a busy time for NEOs, with the Minor Planet Center
Apollo 2009 SH2 was discovered by Gordon Garradd at Siding Spring on Sept. 18th as an 18th mag. object and was due to make a fly-by of Earth within 3 Lunar Distances (LD) by the end of the month. It reached mag +16 when last seen from Great Shefford on Sept. 29th.
Another Apollo 2009 SN103, this one discovered by the Catalina Sky Survey on Sept. 25th was 19th mag., already within 4 LD of Earth and moving at 11"/min. It would reach its closest to Earth (1.2 LD) at about 05h UT on Sept. 28 as it overtook the Earth on its way to perihelion on Oct. 30th. It was observed from Great Shefford 6 hours before closest approach when it had brightened to 16th mag. and had accelerated to a speed of 138"/min. It was also caught the next night in central Gemini, moving slower at 86"/min but with the phase angle increasing very rapidly, it was 18th mag., fading quickly and was a much more difficult target to record.
It is estimated that 2009 SN103 is only about 8 meters in diameter. Another close approach NEO discovered by the Catalina Sky Survey on Sept. 27th and estimated at about 20 meters diameter was 2009 SU104. This Apollo has a very eccentric orbit taking it very close to the orbit of Venus at perihelion, out to 4.2 AU at aphelion. At this apparition it was on its way to perihelion in Nov., crossing the Earth's orbit just after the Earth had passed by. It was observed at its closest at 2.5 LD on Oct 1st when it was mag. 16 and moving east to west at 223"/min in Equuleus.
Several distant artifical satellites were also followed during the month, including LCROSS on Sept. 12th & 16th before it disappeared into southerly declinations until a few days before its impact with the Moon on Oct 9th. The Herschel telescope was also recorded on Sept. 17th at 19th mag. Ephemerides generated from previous astrometry obtained for this object were useless to try and pick it up again as the spacecraft undergoes frequent orbital manoeuvres to keep it near the second Lagrange point (L2). The JPL Horizons ephemeris allowed Herschel to be picked up without problem, moving at 3"/min.
Sunday, 6 September 2009
2009 August notes: 9O0DC57, 2009 QC23 and 2009 QY33
August carried on the very good trend of the first half of 2009, with 18 usable nights providing 96 hours of observing and with plenty of NEO discoveries made by the US based surveys it was a busy month.
On July 30th a fast moving 15th magnitude object found by the Catalina Sky Survey and designated as 9O0DC57 by them was put on the Minor Planet Center's NEO Confirmation page, only to be taken off again the next day with a note "was not a minor planet", normal procedure by the MPC when an artificial satellite is mistakenly picked up as a NEO.
This one though did not match any of the artificial satellites with published orbits. It has a perigee of 18,000Km and an apogee 1/3 the distance to the Moon, making it easily mistaken for a NEO during a close approach.
I followed it over a number of nights during August and on August 2nd managed to determine that it rotates every 5.6 seconds, following it from 00:29 UT into twilight at 03:16 UT. From 00:27 to 01:52 UT it showed a regular 1.5 magnitude variation, but when next picked up at 02:56 UT it was showing a very short flash superimposed on the regular variation, probably less than 1 second long and of about 0.75 magnitudes amplitude. Only about 10 minutes later this flash had increased to about 1.5 magnitudes. The lightcurve is from 495 measurements of 1 second exposures, folded using a period of 5.620 seconds, with the increasing flash marked with curves A and B between phase 0.10 and 0.35. The inset from a 60 second exposure started at 03:21:26 UT shows the object trail 250" long and captures 11 flashes and the secondary maximum can just be made out just to the right of the bright flash.
An 18th mag object moving at 18"/min at discovery and put on the NEO Confirmation page on August 22 turned out to be an very impressive amateur discovery by Noeline Teamo from the Hibiscus Observatory (F84) in Tahiti. Designated 2009 QC23 it was followed at Great Shefford for a week.
Another amateur NEO discovery was made on Aug 27th by the team at the OAM Observatory, La Sagra in Spain, but because it got a low NEO rating by the MPCs automated procedures it never made it onto the NEO Confirmation Page. Team member Reiner Stoss alerted observers that two nights of positions had been obtained and requested further observations via the Minor Planet Mailing List (http://tech.groups.yahoo.com/group/mpml/message/22231). A set of positions obtained just before midnight on Aug 28 from Great Shefford allowed the MPC to announce the new Amor object 2009 QY33 the next day.
On July 30th a fast moving 15th magnitude object found by the Catalina Sky Survey and designated as 9O0DC57 by them was put on the Minor Planet Center's NEO Confirmation page, only to be taken off again the next day with a note "was not a minor planet", normal procedure by the MPC when an artificial satellite is mistakenly picked up as a NEO.
This one though did not match any of the artificial satellites with published orbits. It has a perigee of 18,000Km and an apogee 1/3 the distance to the Moon, making it easily mistaken for a NEO during a close approach.
I followed it over a number of nights during August and on August 2nd managed to determine that it rotates every 5.6 seconds, following it from 00:29 UT into twilight at 03:16 UT. From 00:27 to 01:52 UT it showed a regular 1.5 magnitude variation, but when next picked up at 02:56 UT it was showing a very short flash superimposed on the regular variation, probably less than 1 second long and of about 0.75 magnitudes amplitude. Only about 10 minutes later this flash had increased to about 1.5 magnitudes. The lightcurve is from 495 measurements of 1 second exposures, folded using a period of 5.620 seconds, with the increasing flash marked with curves A and B between phase 0.10 and 0.35. The inset from a 60 second exposure started at 03:21:26 UT shows the object trail 250" long and captures 11 flashes and the secondary maximum can just be made out just to the right of the bright flash.
An 18th mag object moving at 18"/min at discovery and put on the NEO Confirmation page on August 22 turned out to be an very impressive amateur discovery by Noeline Teamo from the Hibiscus Observatory (F84) in Tahiti. Designated 2009 QC23 it was followed at Great Shefford for a week.
Another amateur NEO discovery was made on Aug 27th by the team at the OAM Observatory, La Sagra in Spain, but because it got a low NEO rating by the MPCs automated procedures it never made it onto the NEO Confirmation Page. Team member Reiner Stoss alerted observers that two nights of positions had been obtained and requested further observations via the Minor Planet Mailing List (http://tech.groups.yahoo.com/group/mpml/message/22231). A set of positions obtained just before midnight on Aug 28 from Great Shefford allowed the MPC to announce the new Amor object 2009 QY33 the next day.
Wednesday, 5 August 2009
2009 July notes: (216523) 2001 HY7, 2001 AA50, 2009 NL and 2009 OF
With the short UK nights combined with the summer monsoon starting in the South-West of the US
Aten (216523) 2001 HY7 was observed on three nights in early July, but poor weather prevented getting enough coverage to find an unambiguous rotation period before it had faded out of range by mid-month.
Better luck was had with 2001 AA50, observed on 6 nights between July 20 and Aug 2, which showed an amplitude of 2 magnitudes. A rotation period of just under 26 hours is looking most likely, though a few more nights are still needed to be certain.
Apollo 2009 NL was a LINEAR discovery made on July 13th and was predicted to be magnitude 17 through the rest of the month. Photometry was obtained on 11 nights from July 14-Aug 2 and at magnitude 17-18 the scatter of measurements on individual nights was up to +/- 0.5 magnitudes but even so a likely rotation period of 25.2 hours and an amplitude of about 1 magnitude was able to be derived (see preliminary lightcurve).
2009 OF was another Apollo discovered by LINEAR, this time on July 17th and was initially listed by JPL and NEODys as a virtual impactor. It was observed on four nights from July 19-25, finally being taken off the risk registers on July 26th.
Sunday, 5 July 2009
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.
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 |
Wednesday, 6 May 2009
2009 April notes: 2009 DP2, 2009 HH36, 2009 HU11
Along with the monthly crop of new NEO discoveries followed during April, several other interesting objects were also observed:
2009 DP2 was added to the NEO Confirmation page as a slow moving (0.36"/min) 19th mag object on April 3rd, unusual in that it had already been given a provisional designation by the Minor Planet Center (MPC) some 6 weeks earlier (the D of DP2 indicating it had been designated in the fourth half-month of the year). The MPC had matched the discovery observations from Feb 17 & 20th by the amateur run Observatoire Chante-Perdrix (50 miles north of Marseilles) with new observations from two stations of the Catalina Sky Survey on March 27 and 28 and realized the orbit was unusual enough to warrant posting on the NEOCP. With further positions on April 4th and 5th it was found to be a Centaur with a period of 17 years and perihelion distance of 3.8 AU with aphelion out as far as the orbit of Saturn at 9.5 AU though currently it can't get closer to Saturn than about 1.6 AU.
Another even slower moving NEOCP object, 2009 HH36 also ended up being classified as a Centaur, discovered on April 19th with the 0.9-m telescope of the Steward Observatory on Kitt Peak. A nearby faint field star caused me a few problems when I first observed it on the morning of April 20th. With 2009 HH36 moving at only 0.17"/min it would take an hour to move just 10" and so the star was never far away but by the next night it had moved into clear sky and was much more easily seen.
With observations identified back to March 31 and extending to May 5th the orbit is now given with a period of 45 years and perihelion distance of 7 AU. Aphelion at 18.5 AU is at the distance of Uranus, though again it does not get particularly close to Uranus, but can approach Saturn to about 1 AU. It is currently about 9.5 AU from the Sun and due at perihelion in four years time.
In the images taken for 2009 HH36 on April 20th, another unusually slow moving object (0.30"/min) was seen nearby at about mag +20 and a check of the MPC's Minor Planet Checker web page did not reveal any previously known minor planet candidates in the vicinity. The next night, when following up 2009 HH36, this other object was searched for and found close to its extrapolated position.
I sent off the two nights of observations to the Minor Planet Center, hoping to be assigned discovery credit for a possibly unusual new object, only to find out that it had already been given as a discovery (not surprisingly!) to the Steward Observatory discoverers of 2009 HH36 and had been assigned the designation 2009 HU11. It turned out to be a Jupiter Trojan, fortuitously within just a few arc minutes of the even more distant 2009 HH36 at discovery.
2009 DP2 was added to the NEO Confirmation page as a slow moving (0.36"/min) 19th mag object on April 3rd, unusual in that it had already been given a provisional designation by the Minor Planet Center (MPC) some 6 weeks earlier (the D of DP2 indicating it had been designated in the fourth half-month of the year). The MPC had matched the discovery observations from Feb 17 & 20th by the amateur run Observatoire Chante-Perdrix (50 miles north of Marseilles) with new observations from two stations of the Catalina Sky Survey on March 27 and 28 and realized the orbit was unusual enough to warrant posting on the NEOCP. With further positions on April 4th and 5th it was found to be a Centaur with a period of 17 years and perihelion distance of 3.8 AU with aphelion out as far as the orbit of Saturn at 9.5 AU though currently it can't get closer to Saturn than about 1.6 AU.
Another even slower moving NEOCP object, 2009 HH36 also ended up being classified as a Centaur, discovered on April 19th with the 0.9-m telescope of the Steward Observatory on Kitt Peak. A nearby faint field star caused me a few problems when I first observed it on the morning of April 20th. With 2009 HH36 moving at only 0.17"/min it would take an hour to move just 10" and so the star was never far away but by the next night it had moved into clear sky and was much more easily seen.
With observations identified back to March 31 and extending to May 5th the orbit is now given with a period of 45 years and perihelion distance of 7 AU. Aphelion at 18.5 AU is at the distance of Uranus, though again it does not get particularly close to Uranus, but can approach Saturn to about 1 AU. It is currently about 9.5 AU from the Sun and due at perihelion in four years time.
In the images taken for 2009 HH36 on April 20th, another unusually slow moving object (0.30"/min) was seen nearby at about mag +20 and a check of the MPC's Minor Planet Checker web page did not reveal any previously known minor planet candidates in the vicinity. The next night, when following up 2009 HH36, this other object was searched for and found close to its extrapolated position.
I sent off the two nights of observations to the Minor Planet Center, hoping to be assigned discovery credit for a possibly unusual new object, only to find out that it had already been given as a discovery (not surprisingly!) to the Steward Observatory discoverers of 2009 HH36 and had been assigned the designation 2009 HU11. It turned out to be a Jupiter Trojan, fortuitously within just a few arc minutes of the even more distant 2009 HH36 at discovery.
Tuesday, 7 April 2009
2009 March notes: 2009 DD45, 2009 EW, 2009 FH, 2009 DO111, 2009 FD
March and October are statistically the most likely months for NEOs to be discovered that will make very close passes, within 1 Lunar Distance (LD) of the Earth and this March was no exception.
March got off to a good start with the very close fly-by of NEO 2009 DD45, the picture taken during brief gaps in clouds just after midnight on the 3rd when it was at about 0.9 LD from the Earth. Unusually, it was bright enough to be observed from three days before closest approach (discovery by Rob McNaught at Siding Spring at mag +18.7), reaching mag +10 briefly at its closest when at just 0.18 LD (less than 6 Earth diameters away!), fading to 16th mag by the time I first picked it up, but then still detectable at mag +19 in the rich star fields 10°N of Vega three nights later, somewhat brighter than predicted by the MPC ephemeris.
Even before 2009 DD45 had passed Earth, the next close approach object was queuing up. 2009 EW was discovered by the Catalina Sky Survey on March 2nd and picked up from Great Shefford on March 3.0 and again on March 4.9, before being followed through the night of March 5/6th when it came to within 0.9 LD. It was last detected 30 minutes before closest approach at mag +17, moving at 466"/min, 22° above the northern horizon.
Remarkably, less than two weeks later on March 17th, another NEO, 2009 FH was discovered by Catalina, 28 hours before an encounter that would bring it to within 0.22 LD of Earth. When first picked up at Great Shefford at 19:38 UT on the 17th it was already within 1 LD, mag +15 and moving at the relatively sedate speed of 57"/min. I followed it for 2 hours by which time it was 0.8 LD from Earth and had accelerated to 75"/min. It was last reported at 05:02 UT on 18th March, 7 hours before closest approach, at mag +13 and moving at 250"/min by the Catalina Sky Survey's Mt. Lemmon 1.5-m reflector.
A very preliminary light curve from 220 brightness measurements on March 17th indicates 2009 FH has a rotational period of only 6 minutes 26 seconds, with an amplitude of about 0.3 mags. It made more than 13 full rotations during the 1h 27 minutes the observations span.
There were a number of other objects that made approaches nearly as close as the Moon, notable were 2009 DO111, passing 1.2 LD from Earth early on March 20th, as bright as mag +12 and showing rotational variations of about 1 magnitude by March 19th and also 2009 FD passing at 1.6 LD on March 27, again reaching mag +12. Unusually, this latter object was not discovered by one of the NASA funded surveys but rather by the team operating the La Sagra Observatory in Southern Spain.
March got off to a good start with the very close fly-by of NEO 2009 DD45, the picture taken during brief gaps in clouds just after midnight on the 3rd when it was at about 0.9 LD from the Earth. Unusually, it was bright enough to be observed from three days before closest approach (discovery by Rob McNaught at Siding Spring at mag +18.7), reaching mag +10 briefly at its closest when at just 0.18 LD (less than 6 Earth diameters away!), fading to 16th mag by the time I first picked it up, but then still detectable at mag +19 in the rich star fields 10°N of Vega three nights later, somewhat brighter than predicted by the MPC ephemeris.
Even before 2009 DD45 had passed Earth, the next close approach object was queuing up. 2009 EW was discovered by the Catalina Sky Survey on March 2nd and picked up from Great Shefford on March 3.0 and again on March 4.9, before being followed through the night of March 5/6th when it came to within 0.9 LD. It was last detected 30 minutes before closest approach at mag +17, moving at 466"/min, 22° above the northern horizon.
Remarkably, less than two weeks later on March 17th, another NEO, 2009 FH was discovered by Catalina, 28 hours before an encounter that would bring it to within 0.22 LD of Earth. When first picked up at Great Shefford at 19:38 UT on the 17th it was already within 1 LD, mag +15 and moving at the relatively sedate speed of 57"/min. I followed it for 2 hours by which time it was 0.8 LD from Earth and had accelerated to 75"/min. It was last reported at 05:02 UT on 18th March, 7 hours before closest approach, at mag +13 and moving at 250"/min by the Catalina Sky Survey's Mt. Lemmon 1.5-m reflector.
A very preliminary light curve from 220 brightness measurements on March 17th indicates 2009 FH has a rotational period of only 6 minutes 26 seconds, with an amplitude of about 0.3 mags. It made more than 13 full rotations during the 1h 27 minutes the observations span.
There were a number of other objects that made approaches nearly as close as the Moon, notable were 2009 DO111, passing 1.2 LD from Earth early on March 20th, as bright as mag +12 and showing rotational variations of about 1 magnitude by March 19th and also 2009 FD passing at 1.6 LD on March 27, again reaching mag +12. Unusually, this latter object was not discovered by one of the NASA funded surveys but rather by the team operating the La Sagra Observatory in Southern Spain.
Sunday, 8 March 2009
2009 February notes: 2009 BL58, 2009 BG81, 2009 DS43
Early in February a few fast movers were observed, Apollo 2009 BL58 had been discovered at the end of January by the Catalina Sky Survey. When first observed on 9th Feb it was mag +17.1 and placed 5° SE of Regulus, moving swiftly SE. It was observed two nights later, 45° further on in Hydra at -25° Dec, a degree S of Alpha Corvus and although still mag +17.7, because of its altitude of only 13° was much more difficult to record. It was just a few hours away from its closest to Earth at 4.8 Lunar Distances (LD) and moving at 70"/min.
Apollo 2009 BG81 was a LINEAR discovery from Jan 31st and picked up on the evening of Feb 1st moving at 51"/min, already as close as 4.6 LD but only 19th mag. It came to 4.4 LD on Feb 2nd and was observed by three other observatories but was not reported after that date. With an estimated diameter of 7 metres 2009 BG81 was intrinsically about 4 times smaller than 2009 BL58.
At the end of the month another small Apollo, 2009 DS43 was picked up on 27th Feb in Sextans, first by LINEAR and 97 minutes later by the Catalina Sky Survey (CSS). CSS reported their observations first and were credited with the discovery. It was mag 18 and moving almost due N at 38"/min. I first observed it on the evening of 28th Feb at mag +17.8 by which time it had accelerated to 94"/min and had reached +39° Dec. By then it was at 6.9 LD and would reach its closest at 3am on 1st March at 6.7 LD. By the evening of the 1st it was at a declination of +76° midway between the Pointers and Polaris, had slowed to 81"/min and receded to 7.4 LD and was fading fast, more than 1 mag fainter than the previous night. The Minor Planet Center didn't receive any further reports of it.
Apollo 2009 BG81 was a LINEAR discovery from Jan 31st and picked up on the evening of Feb 1st moving at 51"/min, already as close as 4.6 LD but only 19th mag. It came to 4.4 LD on Feb 2nd and was observed by three other observatories but was not reported after that date. With an estimated diameter of 7 metres 2009 BG81 was intrinsically about 4 times smaller than 2009 BL58.
At the end of the month another small Apollo, 2009 DS43 was picked up on 27th Feb in Sextans, first by LINEAR and 97 minutes later by the Catalina Sky Survey (CSS). CSS reported their observations first and were credited with the discovery. It was mag 18 and moving almost due N at 38"/min. I first observed it on the evening of 28th Feb at mag +17.8 by which time it had accelerated to 94"/min and had reached +39° Dec. By then it was at 6.9 LD and would reach its closest at 3am on 1st March at 6.7 LD. By the evening of the 1st it was at a declination of +76° midway between the Pointers and Polaris, had slowed to 81"/min and receded to 7.4 LD and was fading fast, more than 1 mag fainter than the previous night. The Minor Planet Center didn't receive any further reports of it.
Thursday, 5 February 2009
2009 January notes: 2009 BB77, 2008 YG30, 2008 YY32, 2009 BE, 2009 BJ2, 2009 BD, EPOXI, NeXT
Congratulations to Richard Miles for his first Minor Planet discovery, 2009 BB77 picked up on Jan 30th while he was imaging Comet 17P/Holmes with the Faulkes North telescope!
January provided decent amounts of clear sky at Great Shefford, with 76 hours logged observing. Several NEOs were followed during close approaches, 2008 YG30 was mag +16 and moving at 70"/min on the night of Jan 3rd, 4 Lunar Distances (L.D.) from Earth and due to pass at 3.6 LD the next day. Early on Jan 4th, 2008 YY32 was observed and at 6 LD was already at its closest to Earth, moving at 50"/min and rather fainter at mag +18.2.
After the full moon, on the night of Jan 20th, 2009 BE was seen at mag +17 when it was at 6 LD, but unfortunately cloud prevented it from being observed again, closest approach was on Jan 23rd at 2 LD. The same night another NEO, 2009 BJ2 was imaged but was probably the most challenging object observed in the month. I had followed it the previous two nights but by Jan 20th it was at its closest at 4.7 LD and at its fastest speed of 60"/min. However it had already faded by half a magnitude to mag +19.1 and was very low in the south, in the centre of Canis Major, about 3 degrees SW of M41. The rich Milky Way star-field made identification difficult and the next (cloudy) night was spent discarding many of the 320 images that had been taken when it was masked by stars and then measuring positions from stacks of the remaining images.
Tiny NEO 2009 BD, discovered by the Mt Lemmon 1.5-m reflector of the Catalina Sky Survey on Jan 16th turned out to be quite unusual. It was moving at 10"/min at discovery, but was already only 3 LD from Earth. Over the next 9 days it would gradually drift closer, passing just 1.8 LD from Earth early on Jan 25th and was observed on 5 nights, the last time early on Jan 26th when it was below Polaris, at declination +84°, mag +18.5 and moving at 26"/min. It is probably only about 5 meters in diameter and currently in an orbit very similar to Earth's, with a period of 372 days, an inclination of 1� and a low eccentricity of 0.05. Bill Gray (author of Guide and FindOrb) writes that the available astrometry from Jan 16-26th allows the orbit to be very well determined and shows that it was last in the Earth's vicinity (at a distance of 1.2 LD) around 16 July 1955, with an uncertainty of only about +/- 1 hour! At 01:03 UT on 2nd June 2011 it is due to approach the Earth even closer at a distance of 346,658 Km (= 0.9 LD) with likely uncertainties of just 15 minutes in time and 300 Km in distance. Unfortunately it will then be far south at a declination of -50°, but coming north a few days later when it should be visible once again from northern latitudes.
Two artificial satellites were also observed with a rather unusual connection to each other: On the night of December 30th the EPOXI spacecraft was tracked while at 0.77 LD, at mag +19.2 and moving at 30"/min, midway between Vega and the head of Draco. This was 24 hours after a gravity-assist fly-by of Earth when it had approached to within 50,000Km (= 0.1 LD). EPOXI is the new name for the fly-by spacecraft of the Deep Impact mission that encountered Comet Tempel 1 in 2005 and now on its way to a rendezvous with Comet Hartley 2 in October 2010. The other satellite was the NeXT mission, being the renamed Stardust spacecraft that collected dust samples from Comet Wild 2 in 2004 and has now been re-directed to encounter Comet Tempel 1 in February 2011 to image the crater left by the impactor from Deep Impact! NeXT was seen briefly on the morning of Jan 13th and also followed for 7.5 hours the following night. When last seen it was at 1.1 LD and mag +17, moving at 11"/min, but due to skim just 9,000 Km (= 0.7 Earth diameters!) above the surface of the Earth less than 18 hours later. Unfortunately the close approach night was clouded out.
January provided decent amounts of clear sky at Great Shefford, with 76 hours logged observing. Several NEOs were followed during close approaches, 2008 YG30 was mag +16 and moving at 70"/min on the night of Jan 3rd, 4 Lunar Distances (L.D.) from Earth and due to pass at 3.6 LD the next day. Early on Jan 4th, 2008 YY32 was observed and at 6 LD was already at its closest to Earth, moving at 50"/min and rather fainter at mag +18.2.
After the full moon, on the night of Jan 20th, 2009 BE was seen at mag +17 when it was at 6 LD, but unfortunately cloud prevented it from being observed again, closest approach was on Jan 23rd at 2 LD. The same night another NEO, 2009 BJ2 was imaged but was probably the most challenging object observed in the month. I had followed it the previous two nights but by Jan 20th it was at its closest at 4.7 LD and at its fastest speed of 60"/min. However it had already faded by half a magnitude to mag +19.1 and was very low in the south, in the centre of Canis Major, about 3 degrees SW of M41. The rich Milky Way star-field made identification difficult and the next (cloudy) night was spent discarding many of the 320 images that had been taken when it was masked by stars and then measuring positions from stacks of the remaining images.
Tiny NEO 2009 BD, discovered by the Mt Lemmon 1.5-m reflector of the Catalina Sky Survey on Jan 16th turned out to be quite unusual. It was moving at 10"/min at discovery, but was already only 3 LD from Earth. Over the next 9 days it would gradually drift closer, passing just 1.8 LD from Earth early on Jan 25th and was observed on 5 nights, the last time early on Jan 26th when it was below Polaris, at declination +84°, mag +18.5 and moving at 26"/min. It is probably only about 5 meters in diameter and currently in an orbit very similar to Earth's, with a period of 372 days, an inclination of 1� and a low eccentricity of 0.05. Bill Gray (author of Guide and FindOrb) writes that the available astrometry from Jan 16-26th allows the orbit to be very well determined and shows that it was last in the Earth's vicinity (at a distance of 1.2 LD) around 16 July 1955, with an uncertainty of only about +/- 1 hour! At 01:03 UT on 2nd June 2011 it is due to approach the Earth even closer at a distance of 346,658 Km (= 0.9 LD) with likely uncertainties of just 15 minutes in time and 300 Km in distance. Unfortunately it will then be far south at a declination of -50°, but coming north a few days later when it should be visible once again from northern latitudes.
Two artificial satellites were also observed with a rather unusual connection to each other: On the night of December 30th the EPOXI spacecraft was tracked while at 0.77 LD, at mag +19.2 and moving at 30"/min, midway between Vega and the head of Draco. This was 24 hours after a gravity-assist fly-by of Earth when it had approached to within 50,000Km (= 0.1 LD). EPOXI is the new name for the fly-by spacecraft of the Deep Impact mission that encountered Comet Tempel 1 in 2005 and now on its way to a rendezvous with Comet Hartley 2 in October 2010. The other satellite was the NeXT mission, being the renamed Stardust spacecraft that collected dust samples from Comet Wild 2 in 2004 and has now been re-directed to encounter Comet Tempel 1 in February 2011 to image the crater left by the impactor from Deep Impact! NeXT was seen briefly on the morning of Jan 13th and also followed for 7.5 hours the following night. When last seen it was at 1.1 LD and mag +17, moving at 11"/min, but due to skim just 9,000 Km (= 0.7 Earth diameters!) above the surface of the Earth less than 18 hours later. Unfortunately the close approach night was clouded out.
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