8 orange lights appear and disappear within 3 to 5 seconds west of Yankton.8 different orange lights appearing west of Yankton. Lights would appear then disappear within seconds. Has happened on numerous occasions, clear or cloudy days. The number of lights change on different sighting occasions. Some days there may only be 2 or 3, other days there have been up to 17 or 18 at one given point. The occurence has lasted up to 15 minutes, and the lights just keep appearing and disappearing. There was no aircraft presence seen or heard. Sighting is usually between 8 and 9 p.m. and has no pattern, it just randomally happens.