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         2819        987 
1996         2823       1000 
1997         2819        963 
1998        24484      10300 
1999        13338       5090 
2000        37450      15434 
2001        42951      16894 
2002        40111      16818 
2003        59227      24239 
2004        46395      17699 
2005       310477     139578 
2006       336738     150144 
2007       196328      60736 
2008       113858      32568 
2009        95026      26667 
2010       144940      38637 
2011       152654      41707 
2012       180782      39829 
2013       238464      60440 
2014       533161     130801 
2015       763788     199203 
2016       617834     159477 
2017       530518     144184 
2018       322634      90797 
2019       828803     202501 
2020       554479     140500 
2021       757303     178109 
2022       582415     166844 
2023       530773     151965 
2024       576604     165636 
2025       572092     162329 
2026        93992      25079