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         2807        983 
1996         2817        998 
1997         2798        956 
1998        24467      10295 
1999        13290       5072 
2000        37327      15377 
2001        42815      16832 
2002        39955      16747 
2003        59271      24232 
2004        46215      17625 
2005       309621     139243 
2006       335926     149827 
2007       195752      60590 
2008       112852      32297 
2009        93884      26355 
2010       141871      37883 
2011       151196      41306 
2012       178925      39324 
2013       236050      59769 
2014       533783     131009 
2015       760377     198296 
2016       625987     161751 
2017       526944     143249 
2018       319068      89776 
2019       826183     201891 
2020       547814     138741 
2021       747384     175355 
2022       577023     165310 
2023       526105     150637 
2024       570765     164011 
2025       554542     157214 
2026       212535      41210