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        24481      10299 
1999        13318       5083 
2000        37438      15428 
2001        42924      16881 
2002        40092      16810 
2003        59191      24225 
2004        46352      17684 
2005       310348     139535 
2006       336680     150120 
2007       196182      60697 
2008       113662      32517 
2009        94814      26609 
2010       144840      38610 
2011       152502      41668 
2012       180489      39751 
2013       238076      60334 
2014       532891     130732 
2015       764098     199273 
2016       618039     159540 
2017       530506     144204 
2018       322334      90716 
2019       829825     202850 
2020       553898     140354 
2021       756344     177840 
2022       581604     166613 
2023       530296     151834 
2024       575555     165379 
2025       570827     162219 
2026       124632      32937