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         4451       1536 
1996         3608       1267 
1997         2344        799 
1998        23380       9854 
1999        14679       5633 
2000        40999      17029 
2001        42113      16443 
2002        33465      14935 
2003        62622      25951 
2004        49277      18917 
2005        88404      27125 
2006       114486      36490 
2007       209839      64162 
2008       131284      37272 
2009       106894      29988 
2010       124178      34416 
2011       187551      51856 
2012       173890      48086 
2013       271120      76823 
2014       671992     171397 
2015       770060     204550 
2016       564542     151654 
2017       520878     146146 
2018       412634     115844 
2019       904723     221100 
2020       726768     186680 
2021       934571     224936 
2022       708477     202726 
2023       602204     173330