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        14691       5638 
2000        41033      17045 
2001        42161      16461 
2002        33523      14960 
2003        62671      25971 
2004        49312      18930 
2005        88555      27171 
2006       114680      36544 
2007       210031      64215 
2008       131539      37342 
2009       107128      30051 
2010       124537      34510 
2011       187789      51922 
2012       174258      48190 
2013       271587      76954 
2014       672648     171566 
2015       770892     204766 
2016       557559     149927 
2017       496334     140648 
2018       409406     114989 
2019       856767     209844 
2020       723712     185886 
2021       935383     225128 
2022       709270     202954 
2023       573469     164233