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       336608     150092 
2007       196122      60681 
2008       113605      32502 
2009        94668      26568 
2010       144745      38585 
2011       152317      41618 
2012       180346      39711 
2013       237871      60277 
2014       532642     130663 
2015       764750     199432 
2016       620229     160087 
2017       530160     144110 
2018       322064      90642 
2019       829617     202826 
2020       553766     140342 
2021       755760     177675 
2022       581085     166462 
2023       529905     151724 
2024       575157     165267 
2025       570430     162120 
2026       133168      35128