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         2774        948 
1998        24408      10272 
1999        13184       5035 
2000        37221      15327 
2001        42261      16630 
2002        35799      15341 
2003        58495      23945 
2004        46023      17548 
2005       308748     138918 
2006       335329     149600 
2007       195086      60411 
2008       111919      32043 
2009        92766      26048 
2010       140966      37645 
2011       149799      40923 
2012       177419      38918 
2013       234037      59206 
2014       531407     130498 
2015       756386     197275 
2016       625969     161768 
2017       525268     142850 
2018       313680      88567 
2019       821972     201159 
2020       543324     137643 
2021       737692     172900 
2022       571660     163789 
2023       522292     149565 
2024       566215     162697 
2025       548391     155036 
2026       234966      49007