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        37431      15425 
2001        42917      16878 
2002        40080      16805 
2003        59164      24214 
2004        46339      17679 
2005       310267     139504 
2006       336631     150101 
2007       196129      60683 
2008       113613      32504 
2009        94678      26571 
2010       144752      38587 
2011       152339      41624 
2012       180357      39714 
2013       237896      60284 
2014       532679     130673 
2015       764722     199420 
2016       619549     159928 
2017       530138     144103 
2018       322075      90645 
2019       829666     202838 
2020       553874     140349 
2021       755778     177680 
2022       581110     166470 
2023       529945     151734 
2024       575196     165278 
2025       570534     162140 
2026       133200      35142