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          713        290 
1993         1264        471 
1994         1607        592 
1995         2810        984 
1996         2823       1000 
1997         2804        958 
1998        24481      10299 
1999        13305       5078 
2000        37419      15419 
2001        42907      16873 
2002        40070      16800 
2003        59153      24210 
2004        46319      17671 
2005       310176     139467 
2006       336509     150053 
2007       196079      60669 
2008       113469      32465 
2009        94561      26538 
2010       144660      38562 
2011       152228      41593 
2012       180187      39669 
2013       237627      60209 
2014       533860     130978 
2015       764910     199494 
2016       624774     161388 
2017       530097     144100 
2018       321773      90556 
2019       829335     202745 
2020       553393     140242 
2021       755233     177525 
2022       580665     166343 
2023       529501     151607 
2024       574735     165144 
2025       569563     162040 
2026       360507      39597