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        42159      16460 
2002        33512      14955 
2003        62669      25970 
2004        49307      18928 
2005        88534      27165 
2006       114669      36541 
2007       210009      64209 
2008       131522      37337 
2009       107085      30040 
2010       124447      34486 
2011       187724      51904 
2012       174180      48167 
2013       271531      76937 
2014       672437     171515 
2015       770718     204719 
2016       564940     151762 
2017       520207     146096 
2018       413253     116017 
2019       904435     221045 
2020       727464     186868 
2021       935139     225076 
2022       709154     202920 
2023       605529     174256