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          708        288 
1993         1261        470 
1994         1599        589 
1995         2797        980 
1996         2814        997 
1997         2789        953 
1998        24439      10285 
1999        13254       5060 
2000        37288      15359 
2001        42770      16812 
2002        39890      16726 
2003        59178      24193 
2004        46152      17601 
2005       309310     139133 
2006       335717     149748 
2007       195559      60539 
2008       112440      32183 
2009        93338      26203 
2010       141595      37808 
2011       150792      41194 
2012       178390      39180 
2013       235246      59543 
2014       533719     131103 
2015       759822     198204 
2016       626846     161998 
2017       526759     143227 
2018       315663      89113 
2019       824487     201768 
2020       547291     138674 
2021       744780     174683 
2022       574995     164733 
2023       524623     150219 
2024       569389     163606 
2025       551254     156286 
2026       225263      45880