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          219         78 
1991          864        309 
1992          702        286 
1993         1246        465 
1994         1596        588 
1995         2714        952 
1996         2808        995 
1997         2774        948 
1998        24412      10274 
1999        13190       5037 
2000        37221      15327 
2001        42266      16632 
2002        35803      15343 
2003        58503      23949 
2004        46034      17553 
2005       308801     138941 
2006       335363     149611 
2007       195112      60418 
2008       111934      32047 
2009        92785      26053 
2010       140984      37650 
2011       149846      40936 
2012       177462      38930 
2013       234125      59229 
2014       531491     130520 
2015       756457     197290 
2016       625915     161750 
2017       525096     142803 
2018       313768      88590 
2019       821750     201087 
2020       543484     137688 
2021       737844     172944 
2022       571788     163824 
2023       522381     149590 
2024       566344     162729 
2025       548438     155048 
2026       233434      48589