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        40088      16808 
2003        59164      24214 
2004        46341      17680 
2005       310271     139506 
2006       336649     150108 
2007       196141      60686 
2008       113629      32508 
2009        94689      26574 
2010       144760      38589 
2011       152368      41632 
2012       180374      39719 
2013       237937      60295 
2014       532730     130687 
2015       764483     199356 
2016       618445     159646 
2017       530227     144117 
2018       322122      90658 
2019       829718     202853 
2020       553908     140359 
2021       755848     177699 
2022       581153     166482 
2023       529999     151749 
2024       575217     165284 
2025       570554     162146 
2026       132239      34901