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         2814        997 
1997         2795        955 
1998        24450      10289 
1999        13274       5066 
2000        37298      15363 
2001        42778      16816 
2002        39912      16734 
2003        59192      24199 
2004        46187      17613 
2005       309391     139160 
2006       335776     149770 
2007       195620      60555 
2008       112549      32214 
2009        93509      26252 
2010       141700      37837 
2011       150915      41228 
2012       178595      39234 
2013       235502      59615 
2014       533563     131044 
2015       760406     198351 
2016       626943     162024 
2017       526873     143270 
2018       318434      89598 
2019       825649     201799 
2020       546448     138421 
2021       745403     174853 
2022       575603     164903 
2023       525092     150351 
2024       569835     163732 
2025       554133     156856 
2026       221600      44848