Auroras Come in Different Shapes Arcs : Arcs are long, gracefully curving forms that extend from horizon to horizon. Arcs and bands are the most common auroral forms seen by observers especially common during periods of low solar activity. During moderate to intense solar activity, they become much more active and distorted. Bands : A band is similar to an arc but is more curvy. Arcs can change into bands over the course of a few minutes. Bands are more gracefully curving during low solar activity, but like arcs become more distorted and active during the Sun’s active periods. Corona : A corona is the name for an auroral shape in which the rays appear to converge directly overhead. Coronas are also common during intense solar activity. Rays : Rays appear as smaller filaments or streaks. They are formed when thin arcs curl up on themselves, resulting in a slightly brighter, quickly changing structure. Rays are common during high solar activity.  These are just the most basic forms the aurora can take. In reality, these lights in the sky change from moment to moment, and are brighter during times of intense activity in Earth’s magnetosphere. The shape of an aurora depends partly on where the aurora is occurring relative to the observer, and partly on how Earth’s constantly changing magnetic field responds to the solar wind. If you are fortunate enough to witness this cosmic light show, remember that you are seeing visible evidence of the particles that move along the lines of Earth’s magnetic field.