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         2717        953 
1996         2811        996 
1997         2777        949 
1998        24416      10276 
1999        13225       5049 
2000        37235      15334 
2001        42290      16643 
2002        35814      15351 
2003        58529      23960 
2004        46061      17564 
2005       308914     138986 
2006       335459     149648 
2007       195218      60447 
2008       112068      32081 
2009        92931      26092 
2010       141136      37689 
2011       150049      40993 
2012       177776      39014 
2013       234432      59317 
2014       532101     130680 
2015       757499     197566 
2016       626508     161900 
2017       525673     142965 
2018       314272      88728 
2019       822631     201273 
2020       544542     137978 
2021       739720     173426 
2022       572627     164063 
2023       523029     149768 
2024       567020     162941 
2025       548239     155426 
2026       229963      47343