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         1261        470 
1994         1604        591 
1995         2804        982 
1996         2817        998 
1997         2798        956 
1998        24467      10295 
1999        13290       5072 
2000        37309      15368 
2001        42806      16828 
2002        39943      16741 
2003        59246      24221 
2004        46204      17620 
2005       309584     139229 
2006       335887     149814 
2007       195692      60574 
2008       112815      32287 
2009        93831      26340 
2010       141817      37869 
2011       151137      41288 
2012       178832      39299 
2013       235958      59743 
2014       534197     131142 
2015       760202     198253 
2016       626014     161759 
2017       526767     143206 
2018       318915      89733 
2019       825874     201833 
2020       547368     138635 
2021       746622     175206 
2022       576826     165254 
2023       525869     150574 
2024       570446     163922 
2025       557728     157441 
2026       211395      41320