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         4454       1537 
1996         3608       1267 
1997         2350        801 
1998        23402       9861 
1999        14694       5639 
2000        41037      17047 
2001        42170      16465 
2002        33542      14966 
2003        62698      25981 
2004        49327      18936 
2005        88605      27185 
2006       114774      36572 
2007       210198      64260 
2008       131668      37377 
2009       107219      30075 
2010       124700      34553 
2011       187948      51966 
2012       174577      48275 
2013       271864      77031 
2014       673149     171699 
2015       771339     204887 
2016       558010     150050 
2017       496696     140755 
2018       409814     115101 
2019       857175     209955 
2020       724135     186001 
2021       935856     225236 
2022       709822     203114 
2023       567762     162374