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        14686       5636 
2000        41008      17033 
2001        42138      16451 
2002        33484      14943 
2003        62641      25959 
2004        49301      18926 
2005        88463      27143 
2006       114574      36515 
2007       209908      64181 
2008       131405      37304 
2009       106999      30016 
2010       124332      34457 
2011       187627      51878 
2012       174049      48131 
2013       271302      76875 
2014       672264     171468 
2015       770326     204623 
2016       564592     151674 
2017       519397     145907 
2018       412820     115898 
2019       903172     220727 
2020       727162     186785 
2021       934916     225017 
2022       708838     202826 
2023       604270     173915