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         2347        800 
1998        23392       9857 
1999        14688       5637 
2000        41010      17034 
2001        42138      16451 
2002        33484      14943 
2003        62643      25960 
2004        49301      18926 
2005        88466      27144 
2006       114578      36516 
2007       209908      64181 
2008       131408      37305 
2009       107002      30017 
2010       124344      34459 
2011       187627      51878 
2012       174056      48133 
2013       271310      76877 
2014       672271     171470 
2015       770368     204633 
2016       564579     151671 
2017       519443     145920 
2018       412854     115905 
2019       903218     220737 
2020       727181     186789 
2021       934927     225020 
2022       708850     202830 
2023       604276     173917