Air Glow: Definition and Meaning

Sometimes, most of us must experience, a panoramic light above in the sky. Though this is not a common phenomenon, but nor it is rare; in fact, it can be experienced if you are vigilant about it. It can be seen during the night in a clear sky. So, in this article, we will explore its origin, characteristics, and causes that make it a captivating phenomenon especially for sky-watchers.

What is Air Glow?

Also known as nightglow, air glow is pale and diffuse illumination in the upper atmosphere of the earth, which is usually visible only during the night in the absence of moonlight or any other such artificial light. But one point that need to be understood i.e. it is not auroras or even similar to it. Auroras are charged particles that collide with the earth’s atmosphere, but air glow is different as it originates from different atmospheric activities involving atoms and molecules.

The phenomenon of air glow was first observed in 1868 by a Swedish physicist Anders Angstrom, but it was Simon Newcomb who first scientifically studied and described airglow, in 1901. After that, it has been studied in the laboratory. While understanding it, various chemical reactions have been observed to emit electromagnetic energy as part of the process.

Causes of Air Glow

As we discussed above that air glow is the product of different natural processes that usually occur in the upper atmosphere, especially in the mesosphere and thermosphere. In this region, the incoming solar radiation react with atoms and molecules and causes such glow.

Air glow is a result of several natural processes occurring in the upper atmosphere, predominantly in the mesosphere and thermosphere. These processes lead to the emission of light as atoms and molecules react to incoming solar radiation during the day and night.

Role of Chemical Reactions

During the day time, the Sun’s ultraviolet radiation ionizes the atoms and molecules that present in the upper atmosphere. Because of this process, these atoms and molecules split into the charged particles known as ions and free electrons. Interestingly, in the night, these charged particles i.e. ions and electrons recombine and in the process release energy in the form of visible light. And, this is the light emission that creates the captivating glow in the clear sky.

Some other causes are luminescence caused especially by cosmic rays striking the upper atmosphere, and chemiluminescence caused mainly by oxygen and nitrogen reacting with hydroxyl free radicals at heights of a few hundred kilometres. Though it is not noticeable during the daytime because of the glare and scattering of sunlight.

Role of Atomic Oxygen and Hydroxyl Molecules

Atomic oxygen and hydroxyl (OH) molecules are the most prominent sources of air glow. Atomic oxygen, which readily available in the upper atmosphere, as it is created during the photo-dissociation of molecular oxygen, emits red and green light when it returns to its ground state from the excited states. During this process, the hydroxyl molecules emit a pale blue glow.

Air Glow’s Influence on Astronomy and Space Observation

The air glow has the substantial influence over the astronomical observations and space observations, which usually conducted by satellites and spacecraft. The pale light or glow emitted in this process potentially can interfere with sensitive telescopes and detectors and can affect the ability to study distant stars, galaxies, and other celestial objects. Because of such perceptible influence, astronomers and other scientists consider air glow seriously especially when conducting space missions and designing observational instruments.

Variability and Geographical Distribution

As discussed above, air glow is chemical phenomenon and dependent upon the presence of certain atoms and molecules in the upper atmosphere and also the incoming solar radiation; therefore, its intensity and distribution can vary with time and location. Factors like solar radiation, atmospheric composition, and as well as geomagnetic conditions, all influence the presence, brightness, and color of air glow.

How to See Air Glow?

Though air glow is a regular phenomenon, but it is not always visible. It can be seen only in the clear skies, absolutely free from pollution, cloud, and other artificial lights. Further, it is visible to the naked eyes but only under the optimal conditions. Its fairness often necessitates using long exposure photography or specialized night vision equipment to capture its full splendor.

Difference Between Air Glow and Aurora

This is true that both air glow and aurora emit light in the upper atmosphere, but they have different origins and characteristics. Air glow arises from atmospheric (chemical) processes and emits a pale or faint glow that visible across throughout night sky; whereas, auroras are created by interactions of charged particles (which coming from solar wind) and the earth’s magnetic field. Because of such interactions, vivid and structured light emerges. Secondly, these lights are usually concentrated near the polar regions.

Conclusion

Moreover, air glow is an enchanting mysterious phenomenon that elaborates night sky with its subtle pale blue glow. Its origins lie in the subtle interaction of atoms and molecules in the upper atmosphere, emitting pale or faint light that fascinates observers worldwide. However, as we keep delving into the mysteries of air glow, we keep acquiring a deeper appreciation for the celestial ballet that unfolds above each night.

Frequently Asked Questions

What is air glow, and how is it different from other atmospheric light displays like auroras?

Air glow, also known as nightglow, is a faint illumination of the Earth's night sky caused by various atmospheric processes. It is different from auroras, which result from interactions between charged particles from the solar wind and the Earth's magnetic field, producing more vivid and structured displays typically concentrated near the polar regions.

How does air glow occur in the upper atmosphere?

Air glow occurs due to the interaction of solar radiation with atoms and molecules in the upper atmosphere, particularly in the mesosphere and thermosphere. During the day, the Sun's UV radiation ionizes atoms and molecules, and at night, recombination processes lead to the emission of visible light, creating the ethereal glow in the night sky.

What are the primary sources of air glow's illumination?

Two of the main sources of air glow's illumination are atomic oxygen and hydroxyl (OH) molecules. Atomic oxygen emits red and green light when it returns to its ground state from excited states, while the hydroxyl molecule emits a faint blue glow.

Can air glow affect astronomical observations and space missions?

Yes, air glow can impact astronomical observations and space missions conducted by satellites and spacecraft. The faint light emitted by air glow can interfere with sensitive telescopes and detectors, affecting the study of distant celestial objects. Scientists and astronomers take air glow into account when planning space missions and designing observational instruments.

Is air glow visible to the naked eye, or do you need specialized equipment to observe it?

Air glow is visible to the naked eye under optimal conditions of dark and clear night skies, free from light pollution. However, its faintness often requires using long-exposure photography or specialized night vision equipment to capture its full splendor.

Does air glow vary in intensity and color?

Yes, air glow is a dynamic phenomenon, and its intensity and color can vary with time and location. Factors such as solar activity, atmospheric composition, and geomagnetic conditions influence the brightness and color of air glow.

Where is the best place to observe air glow?

The best place to observe air glow is in areas with minimal light pollution, such as remote rural locations or high-altitude sites with clear and dark night skies.

How does air glow contribute to the beauty of Earth's night sky?

Air glow adds to the mystique and beauty of Earth's night sky with its subtle and enchanting glow. It serves as a reminder of the intricate relationship between our planet and the vast cosmos above.

Can air glow be observed in both hemispheres?

Yes, air glow can be observed in both hemispheres, making it a captivating and universal phenomenon visible to stargazers and skywatchers worldwide.

How does air glow contribute to our understanding of the Earth's atmosphere?

The study of air glow contributes to our understanding of the Earth's upper atmosphere and the various atmospheric processes occurring in the mesosphere and thermosphere. It provides valuable insights into the interactions of atoms and molecules with solar radiation, furthering our knowledge of Earth's atmospheric dynamics.