Direct answer: The northern lights (aurora borealis) happen when charged particles from the Sun interact with Earth's atmosphere near the poles, causing gases like oxygen and nitrogen to glow. Our planet’s magnetic field guides many of these solar particles toward the polar regions, where they collide with atmospheric atoms and molecules, releasing light that we see as shimmering curtains, arcs, and rays in the night sky. What causes them, step by step:

• Solar activity releases charged particles into space (solar wind). During strong solar storms, huge bursts called coronal mass ejections can send more particles toward Earth. These particles travel toward our planet and interact with its magnetic field. [observational context from sources describing solar wind and coronal mass ejections as the primary drivers]
• The Earth’s magnetosphere deflects most particles, but a portion stream toward the magnetic poles, creating the auroral ovals that surround the poles. [magnetic field guidance concept]
• When these energetic particles collide with atoms and molecules in the upper atmosphere (primarily oxygen and nitrogen), the particles transfer energy to the atmospheric atoms, exciting them. When these excited atoms return to their ground state, they emit photons — the visible light of the aurora. [excitation and photon emission mechanism]
• The color and structure arise from the types of atoms involved and the altitude of the interaction: for example, green and red lights are linked to different heights and oxygen transitions, while purples and blues can be tied to nitrogen. The patterns (curtains, rays, and arcs) reflect the shape of Earth’s magnetic field lines and how particles funnel along them. [spectral and altitude considerations]

Where and when you see them:

• Auroras are most commonly visible at high latitudes within the auroral zones near the Arctic and Antarctic. They’re more likely during periods of elevated solar activity and clear, dark skies away from light pollution. [geographic and observational context]
• The best viewing times are often in the local winter months when nights are long and skies are typically darker. Location-specific forecasts can indicate higher chances on given nights. [practical viewing guidance]

If you’d like, I can tailor visibility tips for your location (best months, typical high-activity periods, a simple forecast approach) and explain how to distinguish aurora from other night-sky phenomena.