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          225         80 
1991          867        310 
1992          705        287 
1993         1261        470 
1994         1596        588 
1995         2726        956 
1996         2811        996 
1997         2777        949 
1998        24425      10279 
1999        13231       5051 
2000        37246      15339 
2001        42711      16784 
2002        39854      16706 
2003        59037      24131 
2004        46071      17568 
2005       309001     139024 
2006       335507     149671 
2007       195282      60464 
2008       112115      32094 
2009        92997      26109 
2010       141193      37704 
2011       150100      41007 
2012       177812      39024 
2013       234549      59350 
2014       532300     130730 
2015       757644     197605 
2016       626403     161882 
2017       525926     143026 
2018       314410      88759 
2019       822781     201303 
2020       544726     138025 
2021       740202     173507 
2022       572905     164140 
2023       523231     149826 
2024       567130     162972 
2025       548549     155486 
2026       227527      46582