Northern Lights Sunday May 12: What the different colours mean about the weather

The Northern Lights are set to be visible in the UK once more tonight (Saturday, May 11) with dazzling displays in our skies. This follows an awe inspiring natural show last night that swept the country last night due to an intense geomagnetic storm raging above earth.

But as these beautiful displays appeared in the sky overnight, it left many people wondering why aurora borealis flickered in multiple colours. To answer the question briefly, it's about altitude and oxygen.

Red colours are only visible during periods of the most intense solar activity. This is because the colour is projected by excited atomic oxygen at high altitudes - above 150 miles.

READ MORE: Professor Brian Cox gives hope of 'good chance' we'll see Northern Lights display tonight

Due to the low concentration of oxygen at this high altitude, you can only see red colours in the Northern Lights during these intense storms. Excited atomic oxygen at lower altitudes - up to 150 miles - emits a green colour.

It has a green colour because there is more oxygen at lower altitudes. Lastly, blue and purple colours are created by ionised molecular nitrogen at much lower altitudes of up to 60 miles.

Likewise with red colours, both blue and purple are only seen in the most intense geomagnetic storms. This is oxygen is lower at this altitude, so it's a different reaction altogether which produces these colours.

This weekend a sunspot cluster appears to have merged with each other to become one giant super sunspot 17 times the size of Earth which is firing out massive solar flares and plasma towards our planet. This has meant a G5 "extreme" solar storm was sent earthwards - the highest classification.

When these come into contact with Earth the geomagnetic field interacts with them producing this beautiful ethereal display of colour in our skies. The last time a G5-rated storm hit Earth in October 2003, it caused power outages in Sweden.

Due to this strong storm, multiple colours of the Northern Lights were visible last night. There is a "good chance" that we will experience similar examples of this tonight, according to Professor Brian Cox.

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