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         2347        800 
1998        23397       9859 
1999        14691       5638 
2000        41033      17045 
2001        42157      16459 
2002        33512      14955 
2003        62663      25968 
2004        49307      18928 
2005        88519      27160 
2006       114666      36540 
2007       209975      64200 
2008       131486      37327 
2009       107053      30031 
2010       124417      34478 
2011       187689      51895 
2012       174141      48157 
2013       271480      76922 
2014       672404     171505 
2015       770629     204697 
2016       564848     151739 
2017       520129     146073 
2018       413145     115987 
2019       904332     221015 
2020       727382     186844 
2021       935059     225056 
2022       709052     202889 
2023       604007     173841