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          713        290 
1993         1264        471 
1994         1607        592 
1995         2810        984 
1996         2823       1000 
1997         2804        958 
1998        24481      10299 
1999        13294       5074 
2000        37410      15415 
2001        42907      16873 
2002        40062      16797 
2003        59131      24203 
2004        46310      17668 
2005       310130     139449 
2006       336447     150030 
2007       196032      60657 
2008       113374      32440 
2009        94429      26500 
2010       144610      38550 
2011       152149      41571 
2012       180061      39635 
2013       237404      60149 
2014       534652     131150 
2015       764387     199355 
2016       625609     161627 
2017       529829     144028 
2018       321442      90453 
2019       828913     202628 
2020       552939     140111 
2021       754552     177362 
2022       580172     166200 
2023       528807     151410 
2024       574026     164947 
2025       569184     161963 
2026       238491      40246