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.

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