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          716        291 
1993         1264        471 
1994         1607        592 
1995         2813        985 
1996         2823       1000 
1997         2813        961 
1998        24481      10299 
1999        13316       5082 
2000        37438      15428 
2001        42922      16880 
2002        40088      16808 
2003        59177      24219 
2004        46345      17681 
2005       310306     139518 
2006       336661     150112 
2007       196171      60694 
2008       113629      32508 
2009        94750      26591 
2010       144794      38598 
2011       152431      41649 
2012       180429      39734 
2013       238012      60316 
2014       532782     130704 
2015       764298     199320 
2016       618047     159544 
2017       530323     144151 
2018       322201      90680 
2019       829727     202854 
2020       553889     140352 
2021       756117     177778 
2022       581370     166545 
2023       530137     151788 
2024       575391     165332 
2025       570655     162169 
2026       133879      35277