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.
Sunday, 8 March 2009
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.
Saturday, 6 December 2008
2008 November notes: 2008 VV4 = 2001 XQ, 2004 XK3
With the amount of clear skies in November only amounting to about 40% of that in October, it was a rather disappointing month.
An 18th mag object discovered by the Catalina survey and observed while it was still listed on the NEO Confirmation page on Nov 7th was subsequently given the temporary ID 2008 VV4 and re-observed on Nov 12th by which time JPL was listing it as a "Virtual Impactor" with 17 possible impacts predicted, the first in 2021. While checking for other NEO targets to observe that night I noticed that 2008 VV4 was in the same area of sky and had very similar speed and direction of motion as the Amor object 2001 XQ, as listed on the Minor Planet Center's List of Bright Recovery Opportunities page at http://www.cfa.harvard.edu/iau/NEO/BrightRecovery.html.
2008 VV4 turned out to be the same as the earlier object, 17° from its predicted position and the recovery of 2001 XQ was announced in MPEC 2008-V57. With a period of 6.96 years the circumstances of this apparition were similar to when first discovered in Dec 2001, with the object being at perihelion in early December and moving swiftly south from high northern declinations during November. With the extra 7 years of orbital arc available, JPL was able to calculate that there was no danger of collision with the Earth and it was removed from their risk page at http://neo.jpl.nasa.gov/risk/.
Another object observed while on the NEO Confirmation Page and ending up being a re-discovery of a previously observed object was 2004 XK3. This time it had been picked up by LINEAR as a fast moving 15th mag object and was 14th mag when I observed it only 15 hours later. It was identified within hours by the Minor Planet Center as 2004 XK3 and removed from the NEOCP. With a period of 1.36 years it had done almost exactly three revolutions in the four years since discovery and in fact was only 7° away from the place in the sky where I had observed it four years earlier.
An 18th mag object discovered by the Catalina survey and observed while it was still listed on the NEO Confirmation page on Nov 7th was subsequently given the temporary ID 2008 VV4 and re-observed on Nov 12th by which time JPL was listing it as a "Virtual Impactor" with 17 possible impacts predicted, the first in 2021. While checking for other NEO targets to observe that night I noticed that 2008 VV4 was in the same area of sky and had very similar speed and direction of motion as the Amor object 2001 XQ, as listed on the Minor Planet Center's List of Bright Recovery Opportunities page at http://www.cfa.harvard.edu/iau/NEO/BrightRecovery.html.
2008 VV4 turned out to be the same as the earlier object, 17° from its predicted position and the recovery of 2001 XQ was announced in MPEC 2008-V57. With a period of 6.96 years the circumstances of this apparition were similar to when first discovered in Dec 2001, with the object being at perihelion in early December and moving swiftly south from high northern declinations during November. With the extra 7 years of orbital arc available, JPL was able to calculate that there was no danger of collision with the Earth and it was removed from their risk page at http://neo.jpl.nasa.gov/risk/.
Another object observed while on the NEO Confirmation Page and ending up being a re-discovery of a previously observed object was 2004 XK3. This time it had been picked up by LINEAR as a fast moving 15th mag object and was 14th mag when I observed it only 15 hours later. It was identified within hours by the Minor Planet Center as 2004 XK3 and removed from the NEOCP. With a period of 1.36 years it had done almost exactly three revolutions in the four years since discovery and in fact was only 7° away from the place in the sky where I had observed it four years earlier.
Thursday, 6 November 2008
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.
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.
Thursday, 4 September 2008
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)
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)
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