Topic of the Moment – the northern lights and the solar wind

The aurora borealis – more commonly known as the northern lights – became visible from parts of southern England at the end of February.

Topic of the moment - northern lights and solar wind
Photo credit: NASA


The phenomenon, which most commonly manifests as a fluorescent green glow in the sky, is usually seen at higher latitudes, closer to the magnetic poles, since it’s caused by high-energy charged particles from the Sun colliding with molecules in the Earth’s atmosphere.

The Earth’s magnetic field traps parts of the solar wind as it passes the planet, and the electrons and ions that make up that wind travel towards the Earth’s magnetic poles. Molecules and atoms in the Earth’s upper atmosphere are left ionized or excited by collisions with the particles from the solar wind, and in either regaining an electron or returning to their ground state, they emit light – the glow of the aurora.

Planets with weak magnetic fields – or with none at all – experience the full force of the solar wind, and their atmospheres can be severely thinned or stripped away entirely, leaving the ground without protection from sunlight and making conditions there most hostile to life.

Periods of high solar activity can also damage satellites, particularly those in geosynchronous orbit, since they’re typically higher above the surface.

The astronomer Richard Carrington had first predicted the existence of the solar wind in 1859, and observed the first solar flare the same year. The Voyager 1 space probe found in 2010 that the solar wind extends to nearly 11 billion miles from the Sun – one definition of the edge of our solar system.

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