The Aurora Borealis (and Aurora Australis in the southern hemisphere) is a result of charged particles from the Sun interacting with the Earth’s atmosphere. These particles, primarily electrons and protons, are ejected from the Sun in a stream called the solar wind.
Credit: NASA Goddard Space Flight Center
The NASA mission, Wind launched on Nov. 1, 1994, with the goal of characterizing the constant stream of particles from the sun called the solar wind.
As the solar wind reaches Earth, it’s deflected by our planet’s magnetic field. This field acts like a shield, protecting us from the Sun’s harmful radiation. However, some charged particles get trapped in the magnetic field lines and are funneled towards the poles.
When these particles collide with atoms and molecules in the atmosphere, they transfer energy. The atoms then release that energy as light - photons - as they return to their natural state. These photons are what we see as the aurora.
As solar wind speed increases and the interplanetary magnetic field turns southward, geomagnetic activity rises and the aurora becomes brighter. In general you would want a solar wind speed above 400 km/s and with a strong southerly direction of -10 Bz or lower.
Check our aurora forecast to see how current conditions are looking.
Why Can The Aurora Be Different Colours?
The colour of the aurora depends on the type of atom or molecule that is excited and the energy level of the collision. Different gases at different altitudes produce different colours. Green auroras are caused by collisions with oxygen atoms, red from high altitude oxygen, while hints of purple and blue are caused by collisions with nitrogen.
- Red occurs rarely at around 200-500 km. At this altitude, oxygen is less concentrated and releases photons at a higher frequency than oxygen lower in the atmosphere.
- Green occurs at around 100-300 km above Earth, where oxygen concentrations are high. This is where most collisions happen, and combined with the eye’s sensitivity to green light, it’s the most commonly seen colour.
- Blue and Purple occur below 100 km, caused by interactions with nitrogen molecules. If present, you’ll usually see these colours towards the bottom of the display.
The Aurora Oval
The aurora oval is a ring-shaped area centred around the Earth’s magnetic poles where auroral activity is concentrated.
The brightness within this oval can vary significantly - areas inside may experience vibrant displays, while regions outside may see little to no activity.
The oval is not static. It expands and contracts based on the intensity of solar wind and geomagnetic storms (measured by the Kp-index). During strong solar events, the oval can extend much further south than usual.
The NOAA Ovation map (shown above) is one of the best tools for aurora forecasting. While the Kp-index gives a general idea of geomagnetic activity strength, the Ovation map pinpoints exactly where you might see the aurora.
It uses real-time solar wind and magnetic field data to predict aurora visibility 30 to 40 minutes in advance, including how strong the display will be.
Keep in mind that even if the Ovation map predicts aurora in your area, you still need clear skies and minimal light pollution to see it.