Year Observations     Objects
1858            3          3 
1889            1          1 
1901            1          1 
1920            6          2 
1950            2          1 
1951            6          3 
1953           14          8 
1954           12          5 
1955           14          7 
1956            8          4 
1960            6          3 
1974            2          1 
1975            2          1 
1976            8          4 
1977            2          1 
1978           12          5 
1981           18          5 
1982           13          7 
1983            8          4 
1984            2          1 
1985            8          4 
1986            4          2 
1987            2          1 
1988           38         18 
1990          228         81 
1991          867        310 
1992          713        290 
1993         1261        470 
1994         1604        591 
1995         2804        982 
1996         2817        998 
1997         2798        956 
1998        24464      10294 
1999        13290       5072 
2000        37307      15367 
2001        42804      16827 
2002        39941      16740 
2003        59244      24220 
2004        46204      17620 
2005       309575     139226 
2006       335880     149813 
2007       195688      60573 
2008       112806      32284 
2009        93827      26339 
2010       141809      37867 
2011       151116      41282 
2012       178825      39297 
2013       235937      59738 
2014       534237     131159 
2015       760374     198297 
2016       626077     161778 
2017       526778     143209 
2018       318897      89727 
2019       825911     201848 
2020       547314     138621 
2021       746497     175170 
2022       576746     165231 
2023       525832     150563 
2024       570365     163898 
2025       555796     157167 
2026       210625      41321