CREATE TABLE table_name_72 (object_type VARCHAR(255), ngc_number VARCHAR(255), right_ascension___j2000__ VARCHAR(255))
Name the object type with an NGC number more than 6638 and right ascensions being 18h25m37.8s
    
SQL: SELECT object_type FROM table_name_72 WHERE ngc_number > 6638 AND right_ascension___j2000__ = "18h25m37.8s"