Aurora colors; and the reason they vary from one another?

Green, pink, dark red, blue, purple, and even yellow auroras are all possible!

For countless generations, the captivating natural phenomenon known as the aurora also referred to as the northern lights (aurora borealis) or southern lights (aurora australis), has mesmerized humanity.

This stunning display of shimmering lights near the Earth’s polar regions is a result of the interaction between solar radiation and our planet’s atmosphere. The auroras manifest in a mesmerizing spectrum of colors, including green, pink, blue, and purple, captivating and puzzling observers of the night sky.

However, behind the enchanting chaos of the aurora lies a scientific purpose. In this comprehensive introduction, we explore the causes behind these renowned celestial spectacles and delve into the scientific principles underlying the various colors displayed by the aurora.

Before delving into the multitude of auroral hues, let us briefly revisit the origins of these awe-inspiring phenomena. Auroras are created by the collision of energized solar radiation particles, hurtling at speeds of up to 45 million mph (72 million kph), with the Earth’s upper troposphere. These particles are then guided toward the Earth’s north and south poles by the planet’s magnetic field.

Upon entering the outermost layers of the Earth, these charged particles interact with gas atoms and molecules, resulting in the creation of auroras. This process is analogous to the operation of neon lights: Excited by electrons, the molecules, and atoms in the aurora’s path must release their stored energy as photons of light to return to their original energy state (known as the ground state). Just as the combination of gases inside a neon tube determines the color of the emitted light, the composition of gases in the atmosphere determines the hues of the auroras.

Earth’s atmosphere predominantly comprises nitrogen (78%), oxygen (21%), argon (0.93%), and carbon dioxide (0.04%), along with traces of water vapor, neon, helium, methane, krypton, ozone, and hydrogen.

Further sections will provide a detailed examination of the composition of the atmosphere and the altitude at which solar particles engage with these gases.

Green Aurora:

The most common shade observed in auroras is green. The Canadian Space Agency (CSA) explains that at altitudes ranging from approximately 60 to 190 miles (100 to 300 km) in the Earth’s atmosphere, charged particles interact significantly with oxygen molecules.

The human eye is particularly receptive to the green portion of the color spectrum, which is why we perceive green auroras with greater clarity compared to other colors.

Red Aurora:

Red auroras, although less frequently observed, are commonly associated with heightened solar activity. According to a report from the Canadian Space Agency (CSA), these phenomena occur when solar particles interact with oxygen at higher altitudes, typically ranging from 180 to 250 miles (300 to 400 km).

At these elevated altitudes, the concentration and excitation of oxygen decrease, resulting in a shift to higher frequencies or longer wavelengths, which gives rise to the red color. The upper regions of the aurora display are often the areas where red auroras can be observed.

Blue and Purple Aurora:

Blue and purple auroras, while even rarer, tend to occur during periods of intense solar radiation. The Aurora Zone, a provider of aurora travel experiences, explains that these colors emerge when solar particles collide with nitrogen in the Earth’s atmosphere, specifically at altitudes not exceeding 60 miles.

Typically, the lower segments of the auroral display offer glimpses of blue and purple hues

Yellow and pink aurora:

Pink and yellow auroras are infrequent phenomena that often occur during periods of heightened solar activity. These colors emerge through the blending of red auroras with either green or blue auroras, resulting in unique shades.

The combination of red with green or blue creates the delicate pink and vibrant yellow hues observed in these auroras.

THE ROLE OF SOLAR ACTIVITY

Solar activity, encompassing solar flares and coronal mass ejections, exerts a substantial impact on the intensity, color, and frequency of auroral displays. During periods of heightened solar activity, characterized by the increased bombardment of solar particles on Earth’s atmosphere, the potential for more vibrant and diverse aurora colors becomes amplified.

The sun’s activity follows an 11-year solar cycle, with solar maxima marking periods of maximum activity. Currently, solar cycle 25 is underway, and experts predict that it will reach its peak in 2025, leading to heightened solar activity during this time.