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          225         80 
1991          867        310 
1992          705        287 
1993         1261        470 
1994         1596        588 
1995         2717        953 
1996         2811        996 
1997         2777        949 
1998        24416      10276 
1999        13216       5046 
2000        37233      15333 
2001        42290      16643 
2002        35814      15351 
2003        58524      23958 
2004        46061      17564 
2005       308885     138975 
2006       335446     149644 
2007       195218      60447 
2008       112057      32078 
2009        92920      26089 
2010       141125      37686 
2011       150037      40989 
2012       177750      39007 
2013       234374      59300 
2014       532034     130662 
2015       757430     197549 
2016       626430     161880 
2017       525596     142945 
2018       314219      88715 
2019       822586     201261 
2020       544504     137967 
2021       739640     173404 
2022       572502     164027 
2023       522969     149751 
2024       566994     162934 
2025       548222     155421 
2026       231290      47719