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         1264        471 
1994         1607        592 
1995         2807        983 
1996         2820        999 
1997         2801        957 
1998        24472      10296 
1999        13290       5072 
2000        37374      15398 
2001        42862      16852 
2002        40003      16769 
2003        59414      24293 
2004        46318      17667 
2005       309866     139337 
2006       336176     149922 
2007       196012      60659 
2008       113104      32366 
2009        94206      26440 
2010       144572      38534 
2011       151787      41466 
2012       179521      39487 
2013       236790      59973 
2014       533384     130829 
2015       762559     198872 
2016       626053     161756 
2017       528629     143699 
2018       320346      90138 
2019       827738     202298 
2020       550606     139454 
2021       751052     176407 
2022       579022     165873 
2023       527636     151077 
2024       573195     164703 
2025       558488     158619 
2026       244123      41787