The northern lights are also known as the polar lights. These are the shafts or curtains of colourful lights that are visible in the night sky in the regions located close to the magnetic poles. The scientific names of the northern lights and the southern lights are aurora borealis and aurora australis respectively. The basic process used for the formation of northern lights includes the collision of charged sun particles with the neutral atoms present in the earth’s atmosphere. This leads to the emission of a huge amount of energy in the form of light. The distance at which the northern lights have appeared most closest to the earth is equal to 80 km.
Formation of Northern Lights
The polar lights are formed when the high energy charged particles of the sun escape the sun’s corona, travel through the earth’s atmosphere, and face a series of interactions with the magnetic field of the earth. The corona is the outermost layer of the sun and is considered to be one of its hottest regions. The extensive heat of the sun’s corona region vigorously vibrates the hydrogen and helium atoms present in the sun. This leads to the discharge of millions of electrons and protons in space. These protons and electrons blasted by the sun are polarised and contain a significant amount of charge on them. They move freely in space at a high velocity and are mainly responsible for the creation of the northern lights. The high velocity of the particles helps them escape the sun’s gravitational field and combine with each other to form a cluster of electrically charged gas known as plasma. The gale of plasma is typically known as the solar wind. The solar wind moves towards the earth’s surface at a velocity of approximately one million miles per hour. The earth’s strong magnetic field or the magnetosphere acts as a shield and resists the solar wind from entering the earth’s environment, thereby causing the particles of the solar wind to get deviated around the earth. Meanwhile, the sun blasts another ball of plasma towards the earth. This process is known as coronal mass ejection. The particles of the coronal mass ejection interact with the earth and overpower the magnetosphere. This leads to the creation of a magnetic storm that recoils the magnetosphere back. During the process, some of the particles of the solar wind manage to escape space and enter the upper atmosphere of the earth. The retracting magnetic field tends to drag them towards the regions in the atmosphere known as aurora ovals. Finally, the charged particles, i.e., the electrons and the protons, collide with the neutral atoms of various gases such as oxygen, nitrogen, etc., contained in the earth’s atmosphere. A transfer of energy takes place between the charged solar wind particles and the neutral gas particles. This leads to the emission of photons. The photons are the high energy particles that tend to release their energy in the form of light, thereby producing multiple light waves in the earth’s upper atmosphere, which almost resembles a waterfall of light particles that follow a magnetic field line. This curtain of multi-coloured lights is seen from the earth’s surface and are known as auroras.
Different Colours of Northern Lights
The light curtain formed by the northern lights contains a variety of colours. This is because the earth’s atmosphere is composed of a number of gases such as nitrogen, oxygen, carbon dioxide, etc. The particles of the solar wind tend to interact with different molecules of the air and emit photons. The colours contained by the northern lights typically depend on the wavelength of the emitted photon. In simpler words, the colour of the aurora depends on the type of gas molecule that solar wind particles interact with. Green is the most common colour of the northern lights. The excited atoms of oxygen are typically responsible for the green and red colour of the northern lights. Similarly, the blue colour and deep red hues are produced due to the interaction between sun particles and nitrogen molecules. Also, the altitude at which the polar lights appear has a significant effect on the colour. For instance, the green colour is seen about 100-200 km above the earth’s surface. Similarly, blue and violet colours appear in the regions that are located approximately 100 km higher than the ground, and the red colour occurs above 250 km.
Ideal Conditions for Viewing Northern Lights
1. The formation of northern lights is an astronomical phenomenon, which can be viewed most clearly in places that are located close to the magnetic poles such as northern Canada, northern Scandinavia, northern Russia, etc.
2. The polar lights, i.e., the northern and southern lights are best seen during the nighttime because the auroras are much dimmer during the day and cannot be seen.
3. For the best experience, northern lights must be observed on a clear and dark night.
4. The northern lights are unpredictable in nature; however, late August to early April is the time when the polar lights are most clearly visible.