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        23380       9854 
1999        14684       5635 
2000        41006      17032 
2001        42116      16444 
2002        33469      14937 
2003        62637      25957 
2004        49290      18922 
2005        88453      27140 
2006       114553      36509 
2007       209880      64173 
2008       131367      37294 
2009       106954      30004 
2010       124273      34441 
2011       187604      51871 
2012       173998      48116 
2013       271265      76863 
2014       672142     171438 
2015       770193     204587 
2016       564530     151657 
2017       519431     145903 
2018       412771     115884 
2019       903161     220713 
2020       727014     186748 
2021       934733     224985 
2022       708732     202797 
2023       603782     173783