Year Observations     Objects
1950            2          1 
1951            6          3 
1953            4          2 
1954            2          1 
1955            4          2 
1956            2          1 
1960            6          3 
1974            2          1 
1975            2          1 
1976            8          4 
1977            2          1 
1978            8          3 
1981            4          2 
1982           12          6 
1983            8          4 
1984            2          1 
1985            8          4 
1986            4          2 
1987            2          1 
1988           38         18 
1990           32         14 
1991          532        200 
1992          936        367 
1993         1678        613 
1994         2348        847 
1995         4451       1536 
1996         3608       1267 
1997         2350        801 
1998        23397       9859 
1999        14691       5638 
2000        41033      17045 
2001        42161      16461 
2002        33519      14958 
2003        62671      25971 
2004        49309      18929 
2005        88551      27170 
2006       114680      36544 
2007       210016      64211 
2008       131530      37339 
2009       107101      30044 
2010       124500      34500 
2011       187757      51913 
2012       174220      48179 
2013       271570      76949 
2014       672550     171543 
2015       770863     204758 
2016       565045     151791 
2017       520188     146094 
2018       413308     116030 
2019       904345     221028 
2020       727554     186890 
2021       935300     225109 
2022       709198     202933 
2023       594082     170625