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         2339        844 
1995         4439       1532 
1996         3605       1266 
1997         2337        797 
1998        23368       9849 
1999        14654       5623 
2000        40899      16987 
2001        42011      16397 
2002        33288      14854 
2003        62420      25869 
2004        49049      18824 
2005        87860      26965 
2006       113782      36284 
2007       209106      63960 
2008       130444      37045 
2009       106076      29770 
2010       123003      34097 
2011       186134      51440 
2012       171983      47565 
2013       269224      76314 
2014       668679     170531 
2015       781463     207083 
2016       573248     153649 
2017       536667     148939 
2018       411125     115395 
2019       923788     225774 
2020       723300     185732 
2021       931158     224130 
2022       696977     199375 
2023       648702     186632