Aurora lights up UK skies in a spectacular display

For a few weeks now beyond the spring equinox – marked on 20 March this year – there is evidence of an enhancement to the aurora.

Professor Mike Lockwood, president of the Royal Astronomical Society told BBC Weather that “your chances of seeing aurora at low latitudes is enhanced at the equinoxes because of the Russell-McPherron effect”.

Earth is tilted on an axis of 23.5 degrees. On its orbit around the Sun, that tilt is either towards or away from the Sun at the solstices – which in the northern hemisphere is summer and winter respectively.

At the equinoxes in March and September, Earth is neither tilted towards or away from the Sun in relation to its axis.

This varying Sun-Earth alignment throughout the year results in differences to the amount of solar energy that interacts with Earth’s magnetic field and therefore changes the strength of aurora.

As the solar wind – the stream of energy and particles which have their own magnetic field – interacts with Earth’s magnetic field, a process called magnetic reconnection occurs.

Imagine tiny bar magnets travelling through space that are in the correct north to south orientation so they are attracted to Earth’s magnetic field.

“This reconnection process that lets the energy into Earth’s environment and powers the aurora [facilitated at the equinox] means you get this extra coupling of energy” said Prof Lockwood.

This leads to stronger aurora compared to summer and winter when the alignment is less favourable.

Having the extra energy of an Earth-directed Coronal Mass Ejection and geomagnetic storm will increase chances even more.