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2004 ER21 (Aten making close approach)

Another LINEAR discovery, it was put on the NEO Confirmation Page just before midnight late on 15th March 2004 having been discovered 17 hours earlier. The next night (16th March) the sky was clear at Great Shefford, but by then the area where the object was likely to be found in was already over 3 in size.

LINEAR finally confirmed the object in images taken 24 hours after discovery and this was communicated via the NEO Confirmation Page at 23:00UT on 16th March 2004.

By the time the NEOCP was updated about 1/3 of the uncertainty area had been searched at Shefford. This was stopped immediately and images taken using the ephemeris from the updated NEOCP. Astrometric positions were sent to the MPC at 00:11UT on 17 March 2004 and the announcement Minor Planet Electronic Circular MPEC 2004-F16 was issued 6 hours later, also containing observations from the Klet Observatory (246).

It was followed at Shefford on 4 further nights to 25th March 2004 by which time it had faded to 20th magnitude.

2004 ER21 had passed Earth at 20 lunar distances on 19th March 2004, just a couple of weeks after it had passed aphelion (1.052 AU from Sun), spending most of its time inside the Earth's orbit..


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