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         2339        844 
1995         4439       1532 
1996         3605       1266 
1997         2337        797 
1998        23368       9849 
1999        14654       5623 
2000        40903      16989 
2001        42015      16399 
2002        33295      14857 
2003        62441      25877 
2004        49070      18832 
2005        87893      26976 
2006       113827      36299 
2007       209151      63974 
2008       130509      37063 
2009       106159      29792 
2010       123064      34113 
2011       186199      51458 
2012       172108      47599 
2013       269354      76348 
2014       668954     170600 
2015       781789     207171 
2016       573252     153651 
2017       535176     148647 
2018       410917     115350 
2019       922690     225460 
2020       723425     185765 
2021       931375     224184 
2022       697273     199458 
2023       650032     187013