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         2810        984 
1996         2823       1000 
1997         2807        959 
1998        24481      10299 
1999        13308       5079 
2000        37423      15421 
2001        42911      16875 
2002        40070      16800 
2003        59156      24211 
2004        46322      17672 
2005       310197     139473 
2006       336517     150056 
2007       196087      60671 
2008       113487      32470 
2009        94579      26543 
2010       144697      38572 
2011       152239      41596 
2012       180205      39674 
2013       237686      60226 
2014       533395     130883 
2015       765183     199557 
2016       623980     161160 
2017       529909     144042 
2018       321791      90562 
2019       829321     202741 
2020       553439     140256 
2021       755324     177552 
2022       580734     166363 
2023       529563     151625 
2024       574781     165157 
2025       569724     162058 
2026       354209      38808