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          219         78 
1991          864        309 
1992          675        277 
1993         1222        457 
1994         1593        587 
1995         2708        950 
1996         2802        993 
1997         2771        947 
1998        24404      10270 
1999        13181       5034 
2000        37221      15327 
2001        42256      16628 
2002        35794      15339 
2003        58483      23941 
2004        46017      17546 
2005       308733     138913 
2006       335316     149595 
2007       195075      60408 
2008       111901      32038 
2009        92749      26043 
2010       140935      37637 
2011       149747      40909 
2012       177377      38907 
2013       233972      59187 
2014       531303     130469 
2015       756380     197278 
2016       626628     161957 
2017       525320     142867 
2018       313577      88538 
2019       821901     201144 
2020       543222     137614 
2021       737552     172860 
2022       571585     163767 
2023       522230     149547 
2024       566171     162686 
2025       548322     155019 
2026       237427      49724