​Auroras — the aurora borealis in the north and aurora australis in the south — are among the most breathtaking natural light displays on Earth. These glowing curtains of green, red, purple, and blue light are not merely beautiful; they are the visible result of interactions between the Sun, Earth’s magnetic field, and the upper atmosphere. For an authoritative scientific explanation, NASA provides an excellent overview here:
https://science.nasa.gov/sun/auroras/

Where It All Begins: The Solar Wind

The Sun continuously releases a stream of charged particles known as the solar wind. During periods of heightened solar activity — such as solar flares or coronal mass ejections (CMEs) — this flow becomes faster and more intense. These energetic particles can travel millions of kilometres through space and typically take about two to three days to reach Earth after a major solar event.

Earth’s Magnetic Shield: A Guided Path to the Poles

Earth is protected by a magnetic field generated deep within its core. This magnetic shield, called the magnetosphere, deflects most incoming solar particles. Near the North and South Poles, however, magnetic field lines converge and funnel some particles downward. This is why auroras are most commonly seen in high-latitude regions close to the Arctic and Antarctic Circles.

Collisions in the Upper Atmosphere

As solar particles stream along magnetic field lines, they enter Earth’s upper atmosphere — specifically the ionosphere. This region extends roughly from 80 to 500 kilometres (50 to 310 miles) above Earth’s surface. Here, charged particles collide with atmospheric gases, mainly oxygen and nitrogen. These collisions excite the gas atoms, temporarily boosting their electrons to higher energy states.

When the electrons return to their normal energy levels, they release the excess energy as light — producing the aurora.

Why Auroras Have Different Colours

The colour of an aurora depends on both the type of gas involved and the altitude of the collision:

• Green auroras are the most common and are produced by oxygen at altitudes of about 100–200 km (60–125 mi).

• Red auroras occur higher up, above roughly 200 km (125 mi), also from oxygen.

• Blue and purple auroras are caused by nitrogen molecules, typically at lower altitudes below 100 km (60 mi).

The combination of these emissions creates the layered and sometimes multicoloured displays seen during strong auroral activity.

Movement, Shape, and Space Weather

Auroras are highly dynamic. Their shimmering, rippling motions are driven by changes in solar wind speed and direction, as well as fluctuations in Earth’s magnetic field. During powerful geomagnetic storms, auroras can expand far from the poles and become visible at much lower latitudes than usual.

A Phenomenon Beyond Earth

Auroras are not unique to our planet. NASA has observed auroral activity on other planets such as Jupiter and Saturn, where strong magnetic fields interact with charged particles. Even Mars, despite lacking a global magnetic field, can experience localized auroras under certain conditions.

In Summary

Auroras are the result of an elegant chain of cosmic events: charged particles from the Sun are guided by Earth’s magnetic field into the upper atmosphere, where they collide with gases and release energy as light. Understanding auroras helps scientists study space weather and the ongoing relationship between the Sun and Earth.

For a detailed, NASA-led explanation of auroras and ongoing research, visit:
https://science.nasa.gov/sun/auroras/

​