Majestic auroras have captivated humans for thousands of years. But their nature -- the fact that the lights are electromagnetic and respond to solar activity -- was only realized in the last 150 years. Thanks to coordinated multi-satellite observations and a worldwide network of magnetic sensors and cameras, close study of auroras has become possible over recent decades. Using data from NASA's five THEMIS spacecrafts, scientists have been able to observe and measure Earth's vibrating magnetic field in relation to the northern lights dancing in the night sky over Canada to what up to now has been an undetected rhythm.