Johann Palisa ( December 6 1848 â `` May 2 1925 ) was an Austrian astronomer , born in Troppau in Austrian Silesia ( now in the Czech Republic ) . Johann Palisa ( December 6 , 1848 â `` May 2 , 1925 ) was an Austrian astronomer , born in Opava in Austrian Silesia ( now in the Czech Republic ) .