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         2807        959 
1998        24481      10299 
1999        13313       5081 
2000        37427      15423 
2001        42915      16877 
2002        40072      16801 
2003        59164      24214 
2004        46327      17674 
2005       310214     139480 
2006       336538     150065 
2007       196097      60674 
2008       113530      32481 
2009        94595      26547 
2010       144712      38576 
2011       152254      41600 
2012       180251      39686 
2013       237753      60244 
2014       532967     130774 
2015       765016     199504 
2016       623291     160871 
2017       529922     144044 
2018       321920      90600 
2019       829421     202770 
2020       553599     140301 
2021       755539     177612 
2022       580856     166398 
2023       529669     151656 
2024       574971     165212 
2025       569889     162077 
2026       136105      35911