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          708        288 
1993         1261        470 
1994         1599        589 
1995         2797        980 
1996         2814        997 
1997         2789        953 
1998        24439      10285 
1999        13254       5060 
2000        37288      15359 
2001        42772      16813 
2002        39890      16726 
2003        59178      24193 
2004        46157      17603 
2005       309314     139134 
2006       335724     149751 
2007       195563      60540 
2008       112444      32184 
2009        93341      26204 
2010       141599      37809 
2011       150803      41197 
2012       178412      39186 
2013       235254      59545 
2014       533733     131107 
2015       759859     198214 
2016       626858     162001 
2017       526814     143244 
2018       315680      89118 
2019       824506     201772 
2020       547087     138612 
2021       744824     174697 
2022       575024     164741 
2023       524644     150225 
2024       569412     163613 
2025       551692     156630 
2026       225243      45875