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        24458      10292 
1999        13288       5071 
2000        37303      15365 
2001        42780      16817 
2002        39935      16738 
2003        59202      24203 
2004        46196      17617 
2005       309469     139187 
2006       335815     149787 
2007       195635      60559 
2008       112642      32239 
2009        93600      26277 
2010       141737      37847 
2011       150978      41246 
2012       178653      39250 
2013       235669      59663 
2014       533315     130963 
2015       760629     198409 
2016       626702     161949 
2017       526586     143198 
2018       318605      89646 
2019       825634     201782 
2020       546726     138499 
2021       745744     174953 
2022       576032     165027 
2023       525387     150437 
2024       569906     163769 
2025       554427     156916 
2026       218344      43734