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        23384       9855 
1999        14684       5635 
2000        41006      17032 
2001        42124      16447 
2002        33469      14937 
2003        62639      25958 
2004        49298      18925 
2005        88462      27143 
2006       114567      36513 
2007       209884      64174 
2008       131389      37300 
2009       106991      30014 
2010       124303      34449 
2011       187624      51877 
2012       174042      48129 
2013       271290      76870 
2014       672192     171451 
2015       770267     204608 
2016       564563     151666 
2017       519363     145897 
2018       412792     115891 
2019       902934     220664 
2020       727074     186766 
2021       934797     225002 
2022       708785     202811 
2023       603979     173838