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        13313       5081 
2000        37431      15425 
2001        42915      16877 
2002        40080      16805 
2003        59169      24216 
2004        46335      17677 
2005       310242     139493 
2006       336596     150087 
2007       196119      60680 
2008       113594      32498 
2009        94663      26566 
2010       144742      38584 
2011       152306      41615 
2012       180343      39710 
2013       237863      60276 
2014       532721     130692 
2015       764979     199493 
2016       622015     160527 
2017       530126     144101 
2018       322034      90633 
2019       829557     202809 
2020       553746     140336 
2021       755715     177662 
2022       581046     166451 
2023       529840     151705 
2024       575129     165259 
2025       570183     162105 
2026       134716      35549