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        37442      15430 
2001        42940      16889 
2002        40104      16815 
2003        59215      24235 
2004        46367      17689 
2005       310441     139567 
2006       336721     150138 
2007       196271      60721 
2008       113785      32549 
2009        94951      26647 
2010       144915      38630 
2011       152614      41697 
2012       180653      39795 
2013       238348      60410 
2014       533084     130781 
2015       764236     199312 
2016       618293     159603 
2017       530799     144280 
2018       322531      90772 
2019       829646     202743 
2020       554354     140473 
2021       757003     178027 
2022       582172     166776 
2023       530615     151923 
2024       576183     165557 
2025       571129     162302 
2026        97669      26053