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        40074      16802 
2003        59164      24214 
2004        46329      17675 
2005       310228     139487 
2006       336570     150077 
2007       196105      60676 
2008       113539      32484 
2009        94607      26550 
2010       144719      38578 
2011       152267      41604 
2012       180277      39693 
2013       237771      60249 
2014       532952     130768 
2015       764854     199459 
2016       622863     160754 
2017       529966     144057 
2018       321946      90607 
2019       829447     202778 
2020       553611     140304 
2021       755560     177618 
2022       580871     166402 
2023       529685     151660 
2024       575008     165222 
2025       569956     162082 
2026       135847      35837