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          532        200 
1992          936        367 
1993         1678        613 
1994         2342        845 
1995         4448       1535 
1996         3605       1266 
1997         2344        799 
1998        23370       9850 
1999        14667       5628 
2000        40976      17020 
2001        42092      16433 
2002        33407      14908 
2003        62552      25921 
2004        49227      18896 
2005        88204      27069 
2006       114254      36423 
2007       209603      64097 
2008       131002      37196 
2009       106700      29936 
2010       123770      34299 
2011       187332      51764 
2012       173197      47897 
2013       270659      76700 
2014       671101     171164 
2015       784307     207838 
2016       569046     152665 
2017       529619     147669 
2018       412367     115767 
2019       912244     222925 
2020       725737     186394 
2021       955055     229324 
2022       703219     201168 
2023       654773     188455