As anyone in the UK will already know, the poor weather in May just got worse through June. I suffered the least number of hours observing since December 2002.
The unusual object with provisional designation 6R10DB9 made it's fourth and final perigee in June. Back during the March perigee it was observed with the 10-m SALT telescope and found to have a rotation period of only 2.75 minutes and an amplitude at that time of 1.2 magnitudes. This time it approached from the sunward side of the Earth, passed over the North pole and was picked up again a day after perigee on June 15th in Draco, about 1 degree from Theta Cep while only 0.80 Lunar Distances from Earth, magnitude +19 - +20 and moving at 47"/min. Never 'bright', it was recorded at mag +18.6 on June 18th and at about +19.5 on the 20th, fading again as it receded from both Sun and Earth. The only other observations reported at the time of writing are radar detections from Goldstone on June 12 & 14 and optical astrometry from the 1.5-m Mt Lemmon telescope on June 22. By the end of June it was below 20th mag and too far south to attempt from the UK.
The main indicator that this object is likely to be natural rather than a piece of artificial space junk come from determinations of solar radiation pressure (SRP) acting on it. Bill Gray's FindOrb freeware program includes routines to calculate SRP, given as the area-to-mass ratio or AMRAT in m^2/kg. With astrometry extending for 10 months now, it gives a value of 0.0011, with an RMS residual from 132 observations of 2.5". Not including SRP increases the RMS residual to an unsatisfactory 9.1". The JPL Horizons orbit solution which also includes the Goldstone Radar observations, gives an even smaller value of AMRAT of 0.0007. In comparison, various distant artificial satellites, such as IMP8, Geotail, J002E3 (the piece of old Apollo hardware discovered by Bill Yeung in 2003), WMAP etc have values between 10 and 50 times larger, indicating that 6R10DB9 is much more massive and much less prone to the perturbing effects of SRP than artificial satellites and is therefore likely to be a rocky body, probably about 4 metres in diameter. There is still a chance that time might be spent at some of the large observatories to get spectra and other measurements during July before it goes out of range completely.
Thursday, 5 July 2007
Tuesday, 8 May 2007
2007 April notes: 2007 HV4, Comet C/2007 H2 Skiff, 2007 HB5
April provided at least some observing at the telescope on 20 nights, though a fair proportion were of poor quality with haze or moonlight (or both).
Even so there were some notable objects followed. Apollo 2007 HV4 was confirmed on the NEO Confirmation Page during the evening of April 20th, discovered earlier the same day by the Mt. Lemmon operation of the Catalina Sky Survey. When found it was only 5 times further away than the Moon and a difficult discovery at mag +20.5, moving at 14"/min. When confirmed 16 hours later it had already doubled in apparent speed and was about 1 magnitude brighter. Although never brighter than 18th mag, it was followed over the next two nights reaching a speed of over 180"/min during the evening of April 22nd, 5 hours after passing Earth at 1.4 Lunar Distances.
Another NEO Confirmation Page object observed on the evening of April 19th turned out to be an 18th mag comet (later designated C/2007 H2 Skiff), announced the next day by the Minor Planet Center (MPC) on MPEC 2007-H33. The comet was moving north at 3"/min but later, when the images were checked for other moving objects (by stacking for main belt minor planet motion of 0.5"/min in a westerly direction), a minor planet could be seen about 4' north of the comet. The comet passed a mere 23" west of the minor planet at about 23:00 UT that night.
Using Astrometrica and the MPCs Minor Planet Checker web page it could not be matched with a known object, so the next night the unidentified object was picked up again and the details of both nights were sent off to the MPC. The MPC could not ID it with a known object, assigned it provisional designation 2007 HB5 and gave Great Shefford discovery credit for this main belter. This is a good example of making use of the images taken for a different purpose - on the discovery night five other observatories reported positions for C/2007 H2 around the same time as I did, but only one, Juan Lacruz at La Canada (J87) in Spain also reported positions for 2007 HB5 that night.
Even so there were some notable objects followed. Apollo 2007 HV4 was confirmed on the NEO Confirmation Page during the evening of April 20th, discovered earlier the same day by the Mt. Lemmon operation of the Catalina Sky Survey. When found it was only 5 times further away than the Moon and a difficult discovery at mag +20.5, moving at 14"/min. When confirmed 16 hours later it had already doubled in apparent speed and was about 1 magnitude brighter. Although never brighter than 18th mag, it was followed over the next two nights reaching a speed of over 180"/min during the evening of April 22nd, 5 hours after passing Earth at 1.4 Lunar Distances.
Another NEO Confirmation Page object observed on the evening of April 19th turned out to be an 18th mag comet (later designated C/2007 H2 Skiff), announced the next day by the Minor Planet Center (MPC) on MPEC 2007-H33. The comet was moving north at 3"/min but later, when the images were checked for other moving objects (by stacking for main belt minor planet motion of 0.5"/min in a westerly direction), a minor planet could be seen about 4' north of the comet. The comet passed a mere 23" west of the minor planet at about 23:00 UT that night.
Using Astrometrica and the MPCs Minor Planet Checker web page it could not be matched with a known object, so the next night the unidentified object was picked up again and the details of both nights were sent off to the MPC. The MPC could not ID it with a known object, assigned it provisional designation 2007 HB5 and gave Great Shefford discovery credit for this main belter. This is a good example of making use of the images taken for a different purpose - on the discovery night five other observatories reported positions for C/2007 H2 around the same time as I did, but only one, Juan Lacruz at La Canada (J87) in Spain also reported positions for 2007 HB5 that night.
Friday, 6 April 2007
2007 March notes: 2007 EH, 2007 EK and 6R10DB9
March was an exceptional month for NEO close approaches, with ten objects observed moving faster than 25"/min, and two observed while inside the distance of the Moon.
In the table below "/min is the apparent speed of the object in arcsec/minute and LD = Lunar distance = 0.00257 AU
2007 EH is the fastest natural object I have tracked and is currently the third closest observed approach of a designated minor planet ever (only 2004 FH and 2006 DD1 having had astrometry reported while closer).
It was discovered 44 hours before the close approach and put on the NEO Confirmation page during the afternoon of 9th March, but that evening, with it still unconfirmed I spent some time searching about +/- 0.5 degree around the predicted position but without success. Reviewing the discovery positions from the Catalina Sky Survey, one or two looked somewhat out of step with the others and so an orbit was calculated leaving these out. The resulting prediction was about 1 degree west of the NEOCP prediction and the object was indeed picked up close to that place, allowing the subsequent close approach prediction for the next night to be greatly refined.
The close approach itself was remarkable, to watch images appear on the monitor with the object racing across so fast... at it's fastest speed of 1,250"/min it was 15th mag and covering the field of view of my CCD in 53 seconds, or the diameter of the Moon in less than 1.5 minutes! When first picked up on the evening of the 10th at 19:16 UT it was at RA=11h 41m Dec=+30, reached RA=15h 50m Dec=+60 at 00:45UT on 11th and was last seen at 02:22UT at RA=19h 37m Dec=+50, over 80 degrees of sky covered in less than 7 hours!
Full details of the confirmation, animations from the close approach night and details of the techniques used to measure astrometry of such a fast moving object can be found at http://www.birtwhistle.org/Gallery2007EH.htm.
2007 EK which passed at 0.7 Lunar Distances just two nights after 2007 EH would in a more average month have headlined itself. However, it was nearly two magnitudes fainter than 2007 EH and so was not quite the spectacle of the earlier NEO.
One other noteworthy object seen during the month was 6R10DB9, a Catalina Sky Survey temporary designation given to an object discovered last September which has since then been in geocentric orbit, originally expected to be a small piece of man-made space junk, but increasingly suspected of being natural. It was picked up at mag +19 moving at 24"/min in a dense starfield in Gemini, just 1.2 Lunar Distances from Earth, as it approached it's 2nd to last perigee. It will be perturbed out of the Earth's vicinity for the foreseeable future this coming summer. Attempts to obtain spectra with the 6.5-m MMT during the March perigee were unfortunately clouded out, but there will be one last opportunity in June to try and determine once and for all whether it is indeed a natural object. Some details of the story so far of this interesting object can be found at http://www.birtwhistle.org/Gallery6R10DB9.htm, but hopefully more to come in June and July.
In the table below "/min is the apparent speed of the object in arcsec/minute and LD = Lunar distance = 0.00257 AU
| Object |
March
UT
| "/min |
Distance
AU
|
Distance
LD
|
| 2007 DJ | 01.9 | 30 | 0.021 | 8 |
| 2007 DX40 | 02.1 | 33 | 0.028 | 11 |
| 2007 EH | 11.1 | 1,250 | 0.0011 | 0.4 |
| 2007 EK | 13.2 | 382 | 0.0018 | 0.7 |
| 2007 EV | 15.2 | 42 | 0.016 | 6 |
| 2007 EO88 | 18.8 | 288 | 0.0032 | 1.2 |
| 2007 FC3 | 20.8 | 142 | 0.0090 | 3.5 |
| 2007 FG1 | 22.0 | 25 | 0.025 | 10 |
| 2007 FY20 | 31.9 | 35 | 0.018 | 7 |
| 2006 VV2 | 31.9 | 57 | 0.024 | 9 |
2007 EH is the fastest natural object I have tracked and is currently the third closest observed approach of a designated minor planet ever (only 2004 FH and 2006 DD1 having had astrometry reported while closer).
It was discovered 44 hours before the close approach and put on the NEO Confirmation page during the afternoon of 9th March, but that evening, with it still unconfirmed I spent some time searching about +/- 0.5 degree around the predicted position but without success. Reviewing the discovery positions from the Catalina Sky Survey, one or two looked somewhat out of step with the others and so an orbit was calculated leaving these out. The resulting prediction was about 1 degree west of the NEOCP prediction and the object was indeed picked up close to that place, allowing the subsequent close approach prediction for the next night to be greatly refined.
The close approach itself was remarkable, to watch images appear on the monitor with the object racing across so fast... at it's fastest speed of 1,250"/min it was 15th mag and covering the field of view of my CCD in 53 seconds, or the diameter of the Moon in less than 1.5 minutes! When first picked up on the evening of the 10th at 19:16 UT it was at RA=11h 41m Dec=+30, reached RA=15h 50m Dec=+60 at 00:45UT on 11th and was last seen at 02:22UT at RA=19h 37m Dec=+50, over 80 degrees of sky covered in less than 7 hours!
Full details of the confirmation, animations from the close approach night and details of the techniques used to measure astrometry of such a fast moving object can be found at http://www.birtwhistle.org/Gallery2007EH.htm.
2007 EK which passed at 0.7 Lunar Distances just two nights after 2007 EH would in a more average month have headlined itself. However, it was nearly two magnitudes fainter than 2007 EH and so was not quite the spectacle of the earlier NEO.
One other noteworthy object seen during the month was 6R10DB9, a Catalina Sky Survey temporary designation given to an object discovered last September which has since then been in geocentric orbit, originally expected to be a small piece of man-made space junk, but increasingly suspected of being natural. It was picked up at mag +19 moving at 24"/min in a dense starfield in Gemini, just 1.2 Lunar Distances from Earth, as it approached it's 2nd to last perigee. It will be perturbed out of the Earth's vicinity for the foreseeable future this coming summer. Attempts to obtain spectra with the 6.5-m MMT during the March perigee were unfortunately clouded out, but there will be one last opportunity in June to try and determine once and for all whether it is indeed a natural object. Some details of the story so far of this interesting object can be found at http://www.birtwhistle.org/Gallery6R10DB9.htm, but hopefully more to come in June and July.
Tuesday, 6 March 2007
2007 February notes: 2007 BD7, 2007 BZ48 and 2007 DA61
The first half of February was reasonably favourable with 8 nights used up to the 14th and 49 hours logged, while the last half of the month was very poor, with just 4 cloud interrupted hours logged over 3 nights.
Apollo object 2007 BD7 discovered on 23 Jan 2007 from Lowell was followed on four nights up to 6th Feb as it approached Earth, with it's phase angle reaching about 90 degrees on the last night. It was moving swiftly into evening twilight and with the phase angle continuing to increase and magnitude fading rapidly it was not seen again.
Another Apollo 2007 BZ48, discovered by the Mt. Lemmon Survey in January and making a close approach in February, was also observed on four nights, last seen on the morning of the 7th within hours of it passing Earth at 4.5 Lunar distances at a moderately fast 56"/minute.
The only object imaged from the NEO Confirmation Page in the last half of the month was 2007 DA61, during a half hour gap in the clouds on 25th Feb. This turned out to have a perihelion distance of 2.6 AU, in a highly elliptical orbit, elements available by early March giving P=134 years and indicating perihelion at the beginning of March 2007 (though these values may change somewhat as further positions are obtained). It appeared completely stellar in my images and is likely to be a Damocloid asteroid, but it is possible it might show some signs of outgassing with large instruments in the coming weeks.
Apollo object 2007 BD7 discovered on 23 Jan 2007 from Lowell was followed on four nights up to 6th Feb as it approached Earth, with it's phase angle reaching about 90 degrees on the last night. It was moving swiftly into evening twilight and with the phase angle continuing to increase and magnitude fading rapidly it was not seen again.
Another Apollo 2007 BZ48, discovered by the Mt. Lemmon Survey in January and making a close approach in February, was also observed on four nights, last seen on the morning of the 7th within hours of it passing Earth at 4.5 Lunar distances at a moderately fast 56"/minute.
The only object imaged from the NEO Confirmation Page in the last half of the month was 2007 DA61, during a half hour gap in the clouds on 25th Feb. This turned out to have a perihelion distance of 2.6 AU, in a highly elliptical orbit, elements available by early March giving P=134 years and indicating perihelion at the beginning of March 2007 (though these values may change somewhat as further positions are obtained). It appeared completely stellar in my images and is likely to be a Damocloid asteroid, but it is possible it might show some signs of outgassing with large instruments in the coming weeks.
Tuesday, 6 February 2007
2007 January notes: 2007 AG2 = 2004 BO41, 2007 BD
A LINEAR discovery added to the NEO Confirmation page on 8th Jan was eventually confirmed from Great Shefford 2 days later at +69 degrees declination in the evening sky and followed for four nights over the next two weeks at magnitude +18/19. Given the designation 2007 AG2, it was strangely not followed up by any other observatories. Then on 25th Jan I heard from Sergio Foglia that he had identified 2007 AG2 with the NEO 2004 BO41 which had been discovered by LINEAR and observed from 19-29 Jan 2004 and co-incidentally I had observed on several dates that apparition as a morning object, eventually being lost in the twilight.
I had searched for 2004 BO41 a year after discovery on 3rd Jan 2005, covering about 1 degree of sky. It turns out that the actual position at that time was more than 12 degrees further on, so even 12 months after discovery it was hopelessly lost and by Jan 2007 was many tens of degrees off track.
Another interesting object this month, 2007 BD was discovered by Eric Christensen at the Catalina Sky Survey using the 0.68-m Schmidt. It was only 3 Lunar Distances away and already 17th mag, moving at 27"/min. It passed inside the Moons orbit 32 hours later, reaching a minimum distance from Earth of 0.84 L.D. on 18 Jan 2007 at 02:53UT and was well observed from the Crimea-Nauchnij, Gnosca and Modra observatories and also from the Catalina Sky Survey during the 16 hours it remained inside the Moons orbit. It was last caught from Modra 42 minutes before closest approach, travelling at 303"/min at mag +13.
It was then picked up again from Catalina 52 minutes after closest approach.
Unfortunately, during the close approach I was clouded out, but did manage to catch it 2 nights later when it was still about mag +19 and moving at 11"/min. This is quite unusual to be visible for several days on each side of an approach within the orbit of the Moon. It turns out that 2007 BD is an Aten minor planet with an orbit smaller than the Earth's, taking just 230 days to circle the Sun and with an aphelion distance of 0.986 AU it could be argued to be an Apohele (orbit being entirely inside that of the Earth). However, with the Earth at perihelion in January and the object reaching aphelion literally on the day of close approach, it was overtaken by Earth, passing just 200,000 miles outside the Earths orbit, appearing to approach from almost due East and to recede due West so was therefore almost equally well placed for observers for days either side of close approach.
I had searched for 2004 BO41 a year after discovery on 3rd Jan 2005, covering about 1 degree of sky. It turns out that the actual position at that time was more than 12 degrees further on, so even 12 months after discovery it was hopelessly lost and by Jan 2007 was many tens of degrees off track.
Another interesting object this month, 2007 BD was discovered by Eric Christensen at the Catalina Sky Survey using the 0.68-m Schmidt. It was only 3 Lunar Distances away and already 17th mag, moving at 27"/min. It passed inside the Moons orbit 32 hours later, reaching a minimum distance from Earth of 0.84 L.D. on 18 Jan 2007 at 02:53UT and was well observed from the Crimea-Nauchnij, Gnosca and Modra observatories and also from the Catalina Sky Survey during the 16 hours it remained inside the Moons orbit. It was last caught from Modra 42 minutes before closest approach, travelling at 303"/min at mag +13.
It was then picked up again from Catalina 52 minutes after closest approach.
Unfortunately, during the close approach I was clouded out, but did manage to catch it 2 nights later when it was still about mag +19 and moving at 11"/min. This is quite unusual to be visible for several days on each side of an approach within the orbit of the Moon. It turns out that 2007 BD is an Aten minor planet with an orbit smaller than the Earth's, taking just 230 days to circle the Sun and with an aphelion distance of 0.986 AU it could be argued to be an Apohele (orbit being entirely inside that of the Earth). However, with the Earth at perihelion in January and the object reaching aphelion literally on the day of close approach, it was overtaken by Earth, passing just 200,000 miles outside the Earths orbit, appearing to approach from almost due East and to recede due West so was therefore almost equally well placed for observers for days either side of close approach.
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