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         2348        847 
1995         4451       1536 
1996         3608       1267 
1997         2350        801 
1998        23397       9859 
1999        14694       5639 
2000        41033      17045 
2001        42165      16463 
2002        33531      14963 
2003        62680      25974 
2004        49320      18933 
2005        88562      27173 
2006       114697      36549 
2007       210087      64230 
2008       131592      37357 
2009       107147      30056 
2010       124578      34521 
2011       187838      51935 
2012       174321      48207 
2013       271651      76972 
2014       672842     171617 
2015       771027     204801 
2016       557667     149956 
2017       496438     140681 
2018       409506     115016 
2019       856863     209872 
2020       723802     185909 
2021       935454     225151 
2022       709382     202987 
2023       567536     162332