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         4448       1535 
1996         3605       1266 
1997         2344        799 
1998        23370       9850 
1999        14667       5628 
2000        40976      17020 
2001        42092      16433 
2002        33407      14908 
2003        62552      25921 
2004        49230      18897 
2005        88208      27070 
2006       114257      36424 
2007       209611      64099 
2008       131017      37200 
2009       106711      29939 
2010       123780      34302 
2011       187349      51769 
2012       173235      47907 
2013       270678      76705 
2014       671109     171166 
2015       784339     207846 
2016       568584     152555 
2017       529462     147628 
2018       412317     115753 
2019       911044     222607 
2020       725801     186412 
2021       933694     224724 
2022       704134     201427 
2023       653819     188201