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         2807        983 
1996         2823       1000 
1997         2804        958 
1998        24478      10298 
1999        13294       5074 
2000        37410      15415 
2001        42903      16871 
2002        40060      16796 
2003        59109      24194 
2004        46310      17668 
2005       310108     139441 
2006       336443     150029 
2007       196027      60656 
2008       113366      32438 
2009        94416      26496 
2010       144591      38545 
2011       152139      41568 
2012       180043      39630 
2013       237397      60147 
2014       534589     131135 
2015       764279     199328 
2016       626025     161745 
2017       529704     143996 
2018       321397      90439 
2019       828843     202608 
2020       552830     140079 
2021       754341     177302 
2022       580121     166186 
2023       528731     151390 
2024       573962     164929 
2025       565120     160772 
2026       241119      40962