The autumn equinox arrives on September 22, bringing New England shorter days, cooler nights and something less obvious: better odds of seeing the Northern Lights.

An aurora over Massachusetts still requires the Sun to cooperate. A sufficiently strong solar storm can disturb Earth’s magnetic field and push the Northern Lights far south of their usual polar territory. But around the spring and autumn equinoxes, the geometry of Earth’s magnetic field gives those solar disturbances a little extra help.

Auroras begin with the solar wind, a continuous stream of electrically charged particles, mostly electrons and protons, flowing outward from the Sun. When these particles reach Earth, our magnetic field guides some of their energy toward the polar regions.

There, the particles collide with oxygen and nitrogen high in the atmosphere and transfer energy to them. When the gases release that extra energy, they emit light, producing the shimmering greens, reds, blues and purples of an aurora.

Around the equinoxes, the orientation of Earth’s magnetic field relative to the magnetic field carried by the solar wind makes it easier, on average, for the two to connect. Known as the Russell-McPherron effect, this helps explain why geomagnetic disturbances occur more frequently around March and September than around the solstices.

That gives the Northern Lights an unexpected seasonal rhythm: auroras are statistically more common around the equinoxes.

A spectacular display in New England is never guaranteed. It still takes sufficiently strong activity from the Sun to push the auroral zone this far south. But autumn provides longer, darker nights and somewhat better geomagnetic odds.

For the next few weeks, there is a little more reason than usual to look north.