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 3º 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..