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         3608       1267 
1997         2344        799 
1998        23378       9853 
1999        14674       5631 
2000        40986      17024 
2001        42104      16438 
2002        33440      14923 
2003        62581      25933 
2004        49247      18905 
2005        88280      27089 
2006       114323      36443 
2007       209710      64126 
2008       131175      37243 
2009       106786      29959 
2010       123955      34355 
2011       187478      51802 
2012       173493      47978 
2013       270861      76754 
2014       671515     171270 
2015       784702     207941 
2016       566376     152023 
2017       528434     147411 
2018       412336     115758 
2019       906312     221432 
2020       726189     186522 
2021       934106     224815 
2022       707800     202537 
2023       629892     181510