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        41029      17043 
2001        42157      16459 
2002        33510      14954 
2003        62660      25967 
2004        49307      18928 
2005        88513      27158 
2006       114663      36539 
2007       209955      64194 
2008       131483      37326 
2009       107053      30031 
2010       124413      34477 
2011       187680      51892 
2012       174123      48152 
2013       271465      76918 
2014       672394     171502 
2015       770578     204685 
2016       564814     151731 
2017       519942     146031 
2018       413065     115965 
2019       904077     220947 
2020       727344     186834 
2021       935045     225052 
2022       709030     202882 
2023       604281     173921