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         2342        845 
1995         4445       1534 
1996         3605       1266 
1997         2340        798 
1998        23372       9851 
1999        14660       5625 
2000        40955      17010 
2001        42070      16423 
2002        33372      14892 
2003        62512      25905 
2004        49166      18871 
2005        88079      27031 
2006       114105      36381 
2007       209425      64048 
2008       130858      37156 
2009       106515      29887 
2010       123531      34234 
2011       186919      51650 
2012       172822      47794 
2013       270235      76588 
2014       670337     170960 
2015       783392     207591 
2016       571877     153331 
2017       530756     147831 
2018       411845     115627 
2019       918108     224309 
2020       724878     186158 
2021       932962     224557 
2022       699671     200155 
2023       661121     190183