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       336635     150103 
2007       196129      60683 
2008       113613      32504 
2009        94686      26573 
2010       144756      38588 
2011       152343      41625 
2012       180361      39715 
2013       237907      60287 
2014       532686     130674 
2015       764616     199394 
2016       619082     159810 
2017       530182     144108 
2018       322082      90647 
2019       829684     202843 
2020       553894     140355 
2021       755789     177683 
2022       581128     166475 
2023       529963     151739 
2024       575196     165278 
2025       570548     162144 
2026       132234      34900