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          543        204 
1992          942        370 
1993         1697        620 
1994         2381        859 
1995         4529       1564 
1996         3621       1272 
1997         2385        815 
1998        23463       9887 
1999        14754       5664 
2000        41390      17203 
2001        42521      16613 
2002        33831      15097 
2003        63361      26260 
2004        49864      19146 
2005        89959      27618 
2006       116559      37106 
2007       212626      64924 
2008       134194      38057 
2009       109669      30743 
2010       127459      35296 
2011       191723      52998 
2012       179492      49620 
2013       277393      78598 
2014       683565     174423 
2015       782526     207912 
2016       559810     150849 
2017       481822     137745 
2018       414765     116674 
2019       818831     200959 
2020       729046     187469 
2021       946890     228162 
2022       726123     207641 
2023       550748     157567