The pilot reported that during the cross country night flight he began losing altitude while listening to the automated weather service broadcast for the destination airport. He did not notice the altitude loss. The pilot decided to go to an alternate airport, turned for the alternate, and descended during the turn. At that point he noticed the altitude loss, pulled back on the yoke, and impacted a cornfield. The pilot reported no mechanical malfunctions with the airplane during the accident flight. The pilot's safety recommendation was "haze is deceptive."