The Science of the Northern Lights 

Amazing lights, amazing science

Have you ever seen colours dancing in the night sky and wondered what is happening? The amazing lights of auroras normally appear near the North and South Poles. In the northern hemisphere, we call these the northern lights, or aurora borealis, while in the southern hemisphere they’re called the southern lights, or aurora australis. 

What causes the northern lights?

The Sun is constantly releasing a stream of charged particles that travel away from the Sun on the solar wind. When these particles get close to Earth, they can get caught in Earth’s magnetic field and travel with it toward the poles. When these solar particles collide with ones in Earth’s atmosphere, they release energy in the form of light—ta da, instant auroras!  

What’s special about right now? 

The Sun’s magnetic field flips about every 11 years. In the middle of this cycle, there is an increase in solar activity during which far more charged particles are released than usual. More particles arriving means more chances for auroras to occur. Since the the Sun is at the peak of its activity cycle now, you won’t have another northern light spotting opportunity as good as this one until 2035.   

What makes the northern lights so colourful?  

Auroras paint the skies in greens, pinks and reds—and each colour tells a story about what is happening in Earth’s atmosphere. Two factors that influence the colours of the northern lights are the gases in Earth’s atmosphere and the height where particles meet.  

• Red: When the particles in the solar wind collide with oxygen atoms in the atmosphere 300 to 400 km above the planet, they create red auroras.  
• Green: Green auroras are the most commonly seen. They also happen when the Sun’s charged particles encounter oxygen, this time at heights from 100-300 km above the Earth’s surface.  
• Pink and dark red: Usually seen around the lower edges of an aurora, pinks and dark reds are caused by collisions between the solar wind and nitrogen particles in Earth’s atmosphere. They happen lower in the atmosphere, around the 100 km mark.  
• Blue and purple: These colours, rarer to see, happen when the solar wind meets nitrogen below 100 km. 

Bottom image photo Credits: NASA/SDO