On certain nights in the far north, the sky can put on a show that feels almost unreal. You might see a pale green glow near the horizon that slowly grows into ribbons of light, drifting and curling as if the air itself is moving. That is the aurora borealis, also known as the northern lights, and it happens because Earth is in constant contact with the Sun.

The process starts with the solar wind. The Sun does not just shine light and heat. It also sends out a steady stream of tiny charged particles, mainly electrons and protons, flowing through space. Most of the time, that stream is fairly mild, but the Sun has more energetic moments. During periods of increased activity, it can release stronger bursts of particles and magnetic energy, especially during events like solar flares or coronal mass ejections. When those waves reach Earth, they can stir up stronger auroral displays.

Earth has a magnetic field that acts like a shield, called the magnetosphere. It blocks much of the solar wind, but it also channels some of those charged particles toward the polar regions. The particles follow magnetic field lines down into the upper atmosphere, where they collide with gases like oxygen and nitrogen. Those collisions give the atmospheric atoms and molecules extra energy. They do not hold that energy for long. When they settle back to their normal state, they release the energy as light, and that light is what we see as the aurora.

The colors depend on which gas is involved and how high up the collisions happen. Oxygen is responsible for the most common green aurora, and it can also produce red light at higher altitudes. Nitrogen contributes blues and purples, often appearing in brighter, more active displays or along the lower edges of the green bands. The shapes also vary because the flow of particles and the dynamics of Earth’s magnetic field are constantly changing, so the lights can look like arcs, curtains, or quick pulses that brighten and fade.

As for when you can see the aurora borealis, you need the right combination of location, darkness, and clear skies. Auroras are most frequent within the auroral oval, a ring around Earth’s magnetic pole, so high-latitude places like Alaska, northern Canada, Iceland, and northern Scandinavia tend to have the best odds. They can occur year round, but they are much easier to see in fall, winter, and early spring when nights are long and the sky gets truly dark. Avoiding city lights helps, and so does checking cloud cover. If the Sun is particularly active, the aurora can sometimes drift farther south, surprising people well outside the usual viewing zone.