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         1610        593 
1995         2816        986 
1996         2823       1000 
1997         2813        961 
1998        24484      10300 
1999        13326       5086 
2000        37444      15431 
2001        42940      16889 
2002        40104      16815 
2003        59221      24236 
2004        46367      17689 
2005       310445     139568 
2006       336725     150140 
2007       196291      60726 
2008       113785      32549 
2009        94956      26648 
2010       144915      38630 
2011       152622      41699 
2012       180671      39800 
2013       238360      60413 
2014       533088     130782 
2015       763841     199210 
2016       618306     159605 
2017       530621     144226 
2018       322516      90767 
2019       829397     202670 
2020       554364     140475 
2021       757047     178040 
2022       582200     166784 
2023       530622     151925 
2024       576274     165561 
2025       571714     162302 
2026        95141      25387