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        40897      16986 
2001        42007      16395 
2002        33288      14854 
2003        62412      25866 
2004        49045      18823 
2005        87844      26960 
2006       113774      36282 
2007       209095      63957 
2008       130437      37043 
2009       106051      29763 
2010       122996      34097 
2011       186100      51431 
2012       171956      47558 
2013       269195      76306 
2014       668612     170513 
2015       781423     207071 
2016       573314     153662 
2017       537492     149148 
2018       411326     115439 
2019       924889     226040 
2020       723237     185713 
2021       931124     224121 
2022       696871     199343 
2023       647953     186421