Year Observations     Objects
1950            2          1 
1951            6          3 
1953            4          2 
1954            2          1 
1955            4          2 
1956            2          1 
1960            6          3 
1974            2          1 
1975            2          1 
1976            8          4 
1977            2          1 
1978            8          3 
1981            4          2 
1982           12          6 
1983            8          4 
1984            2          1 
1985            8          4 
1986            4          2 
1987            2          1 
1988           38         18 
1990           32         14 
1991          540        203 
1992          942        370 
1993         1694        619 
1994         2366        854 
1995         4518       1560 
1996         3618       1271 
1997         2382        814 
1998        23451       9882 
1999        14745       5661 
2000        41294      17163 
2001        42431      16578 
2002        33725      15050 
2003        63113      26161 
2004        49710      19083 
2005        89576      27504 
2006       116170      36991 
2007       212084      64775 
2008       133365      37837 
2009       109055      30577 
2010       126711      35098 
2011       190518      52672 
2012       178317      49297 
2013       275593      78097 
2014       679007     173280 
2015       777976     206713 
2016       556851     150061 
2017       479166     136993 
2018       411650     115792 
2019       814312     199724 
2020       725486     186499 
2021       942892     227064 
2022       718014     205447 
2023       550429     157117