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         1599        589 
1995         2797        980 
1996         2814        997 
1997         2783        951 
1998        24434      10283 
1999        13243       5056 
2000        37278      15354 
2001        42760      16807 
2002        39872      16717 
2003        59138      24176 
2004        46116      17586 
2005       309216     139098 
2006       335659     149727 
2007       195452      60510 
2008       112289      32142 
2009        93218      26171 
2010       141413      37761 
2011       150498      41115 
2012       178142      39113 
2013       235032      59485 
2014       533159     130953 
2015       758913     197957 
2016       626307     161853 
2017       526343     143112 
2018       315119      88958 
2019       823696     201545 
2020       546402     138427 
2021       743006     174224 
2022       574246     164522 
2023       524128     150080 
2024       568466     163349 
2025       549030     155620 
2026       227740      46691