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         2810        960 
1998        24481      10299 
1999        13316       5082 
2000        37431      15425 
2001        42915      16877 
2002        40080      16805 
2003        59164      24214 
2004        46337      17678 
2005       310263     139502 
2006       336604     150091 
2007       196122      60681 
2008       113605      32502 
2009        94668      26568 
2010       144745      38585 
2011       152317      41618 
2012       180346      39711 
2013       237867      60276 
2014       532638     130662 
2015       764809     199447 
2016       620949     160257 
2017       530177     144114 
2018       322049      90637 
2019       829614     202825 
2020       553766     140342 
2021       755753     177673 
2022       581085     166462 
2023       529905     151724 
2024       575157     165267 
2025       570419     162117 
2026       133225      35146