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         2813        961 
1998        24481      10299 
1999        13316       5082 
2000        37438      15428 
2001        42920      16879 
2002        40088      16808 
2003        59169      24216 
2004        46345      17681 
2005       310303     139517 
2006       336651     150109 
2007       196152      60689 
2008       113629      32508 
2009        94714      26581 
2010       144787      38596 
2011       152392      41638 
2012       180385      39722 
2013       237976      60306 
2014       532762     130697 
2015       764455     199350 
2016       617979     159526 
2017       530257     144127 
2018       322152      90666 
2019       829745     202860 
2020       553836     140337 
2021       755942     177728 
2022       581208     166498 
2023       530076     151770 
2024       575298     165306 
2025       570614     162158 
2026       133189      35115