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         2348        847 
1995         4451       1536 
1996         3608       1267 
1997         2344        799 
1998        23380       9854 
1999        14679       5633 
2000        41004      17031 
2001        42116      16444 
2002        33467      14936 
2003        62632      25955 
2004        49282      18919 
2005        88422      27131 
2006       114517      36499 
2007       209859      64167 
2008       131296      37275 
2009       106920      29995 
2010       124238      34432 
2011       187582      51865 
2012       173933      48098 
2013       271163      76835 
2014       672073     171419 
2015       770107     204563 
2016       564478     151639 
2017       519760     145948 
2018       412710     115866 
2019       904143     220955 
2020       726879     186710 
2021       934617     224951 
2022       708544     202745 
2023       602392     173384