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         2813        985 
1996         2823       1000 
1997         2813        961 
1998        24484      10300 
1999        13318       5083 
2000        37440      15429 
2001        42934      16886 
2002        40104      16815 
2003        59202      24230 
2004        46358      17686 
2005       310395     139551 
2006       336709     150133 
2007       196240      60713 
2008       113751      32540 
2009        94915      26637 
2010       144878      38620 
2011       152574      41687 
2012       180575      39774 
2013       238265      60387 
2014       533005     130760 
2015       764162     199296 
2016       618212     159582 
2017       530700     144258 
2018       322461      90752 
2019       830059     202905 
2020       554167     140428 
2021       756778     177966 
2022       581942     166709 
2023       530516     151896 
2024       575959     165492 
2025       570987     162264 
2026       107381      28479