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         2810        960 
1998        24481      10299 
1999        13316       5082 
2000        37431      15425 
2001        42917      16878 
2002        40083      16806 
2003        59164      24214 
2004        46341      17680 
2005       310269     139505 
2006       336638     150104 
2007       196137      60685 
2008       113613      32504 
2009        94689      26574 
2010       144760      38589 
2011       152347      41626 
2012       180368      39717 
2013       237903      60286 
2014       532699     130678 
2015       764566     199379 
2016       618720     159714 
2017       530182     144107 
2018       322092      90650 
2019       829671     202839 
2020       553893     140355 
2021       755822     177692 
2022       581141     166478 
2023       529966     151740 
2024       575199     165279 
2025       570544     162143 
2026       132234      34899