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          716        291 
1993         1264        471 
1994         1607        592 
1995         2813        985 
1996         2823       1000 
1997         2807        959 
1998        24481      10299 
1999        13313       5081 
2000        37425      15422 
2001        42915      16877 
2002        40070      16800 
2003        59159      24212 
2004        46322      17672 
2005       310207     139477 
2006       336536     150064 
2007       196094      60673 
2008       113526      32480 
2009        94595      26547 
2010       144708      38575 
2011       152247      41598 
2012       180247      39685 
2013       237744      60242 
2014       532999     130785 
2015       765152     199543 
2016       623112     160941 
2017       529894     144039 
2018       321910      90597 
2019       829405     202765 
2020       553581     140296 
2021       755531     177610 
2022       580848     166396 
2023       529665     151655 
2024       574961     165209 
2025       569860     162073 
2026       136139      35920