Strange balls or patches of light whose existence and behavior are sometimes difficult to explain. They are usually white or yellow, but other colors have been seen. Sometimes they appear in the same locality, off and on, for years; and sometimes they appear only once or for a short time. In the United States there are three long-established and persistent sets of lights. The Marfa lights were first observed near Marfa, Texas, by Robert Ellison in 1883. Another set of lights near Joplin, Missouri, appear regularly. A third set, the brown mountain lights, has been seen near Morganton, North Carolina, since 1913.