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         2810        960 
1998        24481      10299 
1999        13316       5082 
2000        37433      15426 
2001        42917      16878 
2002        40088      16808 
2003        59164      24214 
2004        46341      17680 
2005       310289     139512 
2006       336651     150109 
2007       196149      60688 
2008       113629      32508 
2009        94703      26578 
2010       144772      38592 
2011       152376      41634 
2012       180385      39722 
2013       237952      60299 
2014       532753     130694 
2015       764463     199351 
2016       618242     159597 
2017       530243     144120 
2018       322137      90662 
2019       829779     202870 
2020       553913     140361 
2021       755895     177714 
2022       581184     166491 
2023       530050     151762 
2024       575258     165295 
2025       570593     162152 
2026       131980      34850