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        42915      16877 
2002        40080      16805 
2003        59164      24214 
2004        46337      17678 
2005       310263     139502 
2006       336612     150093 
2007       196122      60681 
2008       113609      32503 
2009        94668      26568 
2010       144749      38586 
2011       152328      41621 
2012       180354      39713 
2013       237874      60278 
2014       532665     130669 
2015       764744     199429 
2016       620018     160033 
2017       530102     144093 
2018       322071      90644 
2019       829627     202829 
2020       553773     140344 
2021       755767     177677 
2022       581091     166464 
2023       529908     151725 
2024       575174     165272 
2025       570497     162134 
2026       133227      35145