Criteria Defining these Tables and Charts were Revised on November 30, 2006
The following charts and tables have been revised to reflect improved estimates
for near-Earth asteroid (NEA) reflectivities (albedos) - and hence
diameters. The
absolute magnitude of a NEA (H) is a measure of the object's brightness one
astronomical unit from the sun and Earth and at zero phase angle (i.e., the
angle between the sun and Earth, as seen from the NEA, is zero). The
absolute magnitude (H) for a particular NEA is computed from the observed
apparent magnitudes of the object at various times when the phase angles
and the distances from the sun and Earth are known. A value for H can then
be converted to an effective diameter using an assumed value for the NEA's
reflectivity (albedo). An effective diameter is the diameter of a
hypothetical spherical NEA that would provide the same apparent brightness
as the observed NEA, whose actual shape is unknown.
Until relatively recently, the mean albedo for NEAs was thought to be 0.11 so
the corresponding absolute magnitude for a NEA whose effective diameter is one
kilometer was thought to be H = 18.0. Tables and charts based upon H = 18.0
have been provided on this web site since its inception and these charts can
still be viewed at the following link.
Recent work by Stuart (2003) and others have shown that NEAs are, in the mean,
20% brighter than previously thought so that the mean albedo for NEAs is
0.14 rather than 0.11. Using this revised mean albedo implies the absolute
magnitude (H) for a NEA with an effective one kilometer diameter is 17.75.
The charts and plots given below reflect this recent update.
Stuart, J.S. (2003). Observational Constraints on the Number, Albedos, Sizes,
and Impact Hazards of the Near-Earth Asteroids. Ph.D. thesis, MIT.
All Asteroids
Table 1. NEAs Discovered by Site
Half Year Intervals |
LINEAR (704) |
NEAT (566,608,644) |
Spacewatch (691,291) |
LONEOS (699) |
Catalina (703,E12,G96) |
Other | Cumulative Total |
1995 (1) | 0 | 0 | 14 | 0 | 0 | 4 | 335 |
1995 (2) | 0 | 0 | 12 | 0 | 0 | 2 | 349 |
1996 (1) | 1 | 5 | 18 | 0 | 0 | 4 | 377 |
1996 (2) | 0 | 5 | 10 | 0 | 0 | 2 | 394 |
1997 (1) | 3 | 2 | 10 | 0 | 0 | 4 | 413 |
1997 (2) | 14 | 9 | 4 | 0 | 0 | 7 | 447 |
1998 (1) | 44 | 9 | 19 | 1 | 1 | 7 | 528 |
1998 (2) | 92 | 2 | 16 | 6 | 2 | 6 | 652 |
1999 (1) | 74 | 0 | 12 | 7 | 11 | 1 | 757 |
1999 (2) | 87 | 0 | 7 | 7 | 19 | 3 | 880 |
2000 (1) | 108 | 2 | 14 | 21 | 13 | 4 | 1042 |
2000 (2) | 150 | 14 | 12 | 17 | 0 | 8 | 1243 |
2001 (1) | 95 | 28 | 7 | 22 | 0 | 2 | 1397 |
2001 (2) | 182 | 64 | 15 | 20 | 0 | 4 | 1682 |
2002 (1) | 158 | 54 | 16 | 14 | 1 | 6 | 1931 |
2002 (2) | 128 | 88 | 6 | 7 | 0 | 5 | 2165 |
2003 (1) | 102 | 30 | 24 | 34 | 0 | 8 | 2363 |
2003 (2) | 133 | 38 | 33 | 20 | 8 | 8 | 2603 |
2004 (1) | 167 | 19 | 41 | 14 | 25 | 6 | 2875 |
2004 (2) | 137 | 7 | 29 | 25 | 60 | 6 | 3139 |
2005 (1) | 78 | 8 | 28 | 22 | 116 | 10 | 3401 |
2005 (2) | 59 | 30 | 54 | 19 | 193 | 10 | 3766 |
2006 (1) | 44 | 4 | 45 | 13 | 197 | 3 | 4072 |
2006 (2) | 52 | 18 | 54 | 6 | 200 | 5 | 4407 |
2007 (1) | 38 | 4 | 20 | 7 | 200 | 3 | 4679 |
2007 (2) | 73 | 0 | 25 | 5 | 266 | 7 | 5055 |
2008 (1) | 74 | 0 | 43 | 1 | 284 | 5 | 5462 |
2008 (2) | 67 | 0 | 43 | 0 | 280 | 11 | 5863 |
2009 (1)* | 0 | 0 | 2 | 0 | 10 | 0 | 5875 |
* Incomplete half-year (based on discovery data through 2009-Jan-09 06:00 local)
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Large Asteroids
Table 2. Large NEAs Discovered by Site
Half Year Intervals |
LINEAR (704) |
NEAT (566,608,644) |
Spacewatch (691,291) |
LONEOS (699) |
Catalina (703,E12,G96) |
Other | Cumulative Total |
1995 (1) | 0 | 0 | 3 | 0 | 0 | 2 | 175 |
1995 (2) | 0 | 0 | 4 | 0 | 0 | 1 | 180 |
1996 (1) | 0 | 2 | 2 | 0 | 0 | 0 | 184 |
1996 (2) | 0 | 2 | 0 | 0 | 0 | 0 | 186 |
1997 (1) | 0 | 1 | 2 | 0 | 0 | 1 | 190 |
1997 (2) | 2 | 3 | 1 | 0 | 0 | 2 | 198 |
1998 (1) | 8 | 4 | 2 | 1 | 0 | 1 | 214 |
1998 (2) | 23 | 2 | 1 | 3 | 0 | 3 | 246 |
1999 (1) | 17 | 0 | 2 | 5 | 3 | 0 | 273 |
1999 (2) | 24 | 0 | 0 | 1 | 2 | 2 | 302 |
2000 (1) | 30 | 2 | 0 | 1 | 4 | 1 | 340 |
2000 (2) | 39 | 2 | 3 | 3 | 0 | 4 | 391 |
2001 (1) | 24 | 8 | 0 | 3 | 0 | 0 | 426 |
2001 (2) | 22 | 5 | 0 | 4 | 0 | 1 | 458 |
2002 (1) | 30 | 4 | 2 | 3 | 0 | 1 | 498 |
2002 (2) | 20 | 10 | 0 | 1 | 0 | 1 | 530 |
2003 (1) | 15 | 3 | 1 | 6 | 0 | 1 | 556 |
2003 (2) | 17 | 5 | 1 | 4 | 1 | 1 | 585 |
2004 (1) | 14 | 5 | 1 | 2 | 2 | 1 | 610 |
2004 (2) | 8 | 1 | 0 | 1 | 13 | 0 | 633 |
2005 (1) | 10 | 0 | 2 | 1 | 9 | 1 | 656 |
2005 (2) | 6 | 5 | 4 | 0 | 9 | 1 | 681 |
2006 (1) | 3 | 0 | 2 | 1 | 9 | 0 | 696 |
2006 (2) | 1 | 0 | 3 | 0 | 12 | 0 | 712 |
2007 (1) | 2 | 0 | 3 | 0 | 9 | 1 | 727 |
2007 (2) | 5 | 0 | 1 | 0 | 7 | 0 | 740 |
2008 (1) | 2 | 0 | 1 | 0 | 9 | 0 | 752 |
2008 (2) | 3 | 0 | 1 | 0 | 6 | 0 | 762 |
2009 (1)* | 0 | 0 | 1 | 0 | 0 | 0 | 763 |
* Incomplete half-year (based on discovery data through 2009-Jan-09 06:00 local)
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Data compiled by Alan Chamberlin.
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