What causes the Northern Lights (auroras)?

Auroras form when charged particles streaming from the Sun, carried by the solar wind, get funneled by Earth's magnetic field toward the poles and collide with gas molecules high in the atmosphere. These collisions excite the gas atoms, and as they settle back down they release energy as light, producing the shimmering curtains we see. Oxygen typically glows green or red depending on altitude, while nitrogen tends to produce blue or purplish hues, which is why the colors shift.

Moonlight bending in clouds just produces ordinary halos or glows around the moon, nothing like the moving, colored curtains of an aurora. Light reflecting off the ocean is simple mirror-like reflection and does not involve the atmosphere or solar particles at all.

Because this depends on Earth's magnetic field, auroras are strongest near the poles, but unusually powerful solar storms can push them far enough south (or north) to be seen at surprisingly low latitudes for a night or two.