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         2814        997 
1997         2798        956 
1998        24464      10294 
1999        13290       5072 
2000        37303      15365 
2001        42782      16818 
2002        39938      16739 
2003        59206      24205 
2004        46199      17618 
2005       309491     139195 
2006       335822     149790 
2007       195653      60564 
2008       112655      32243 
2009        93664      26294 
2010       141745      37849 
2011       151004      41253 
2012       178693      39261 
2013       235723      59678 
2014       533398     130986 
2015       760355     198336 
2016       626502     161892 
2017       526575     143195 
2018       318661      89662 
2019       825607     201773 
2020       546960     138539 
2021       745863     174988 
2022       576143     165057 
2023       525468     150460 
2024       570005     163797 
2025       554544     156945 
2026       218191      43646